Subject: GLOWBUGS digest 438

From: [email-masked]
Date: Thu, 6 Feb 1997 18:36:14 GMT

GLOWBUGS Digest 438

Topics covered in this issue include:

  1) Ancient knowledge; class C grid impedence
	by [email-masked]
  2) Re: 70V PA output transformers
	by [email-masked] (michael silva)
  3) Re: Ancient knowledge; class C grid impedence
	by [email-masked]
  4) 70v Transformers - another question
	by Dave <[email-masked]>
  5) Re: Radio Swap Meet
	by [email-masked] (Brian Carling G3XLQ/AF4K)
  6) Re: 70v Transformers - another question
	by [email-masked] (Jeff Duntemann)
  7) Re: 624 Kits / a source of rocks
	by [email-masked] (Brian Carling G3XLQ/AF4K)
  8) Even more thoughts re: 1843.2 kc
	by Jeffrey Herman <[email-masked]>
  9) Re: Top Band Frequency
	by "Brian Carling" <[email-masked]>
 10) Tube base removal
	by [email-masked] (John Heck)
 11) Re[2]: Top Band Frequency
	by [email-masked]
 12) Re: Tube base removal
	by [email-masked] (Jeff Duntemann)
 13) Re: 70V PA output transformers
	by Roy Morgan <[email-masked]>
 14) Re: Re[2]: Top Band Frequency
	by [email-masked] (Jeff Duntemann)
 15) Re: Tube base removal
	by Roy Morgan <[email-masked]>
 16) R-392 assistance!
	by "KASTIGAR, MATTHEW (M" <[email-masked]>
 17) Re[4]: Top Band Frequency
	by [email-masked]
 18) Re: Tube base removal
	by [email-masked] (William H. Launer)
 19) Audio impedance matching
	by [email-masked] (William Hawkins)
 20) Re: Tube base removal
	by [email-masked] (Wouter de Waal)

----------------------------------------------------------------------

Date: Wed, 5 Feb 97 13:02:21 CST
From: [email-masked]
To: [email-masked]
Subject: Ancient knowledge; class C grid impedence
Message-ID: <[email-masked]>

Situation: trying to drive a P-P, class C amp, link coupled input, with an
exciter designed for 50-70 ohm load.

Problem: appearent impedence mismatch causing "rough" sounding tone on a
monitoring receiver. Plenty of driving watts available.

Experiment: I coupled the amp to the exciter through a small antenna tuner
and was able to get good sounding tone. Grid current indicates same DC
values whether tone is rough or smooth, and output of amp is same also,
regardless of tone. BTW, I can't tell which direction the antenna tuner
is transforming the impedence.

I refered to the Wm. Orr texts on class C amplifier design and his calcu-
lations all require detail data from tube curve charts to resolve input
impedence. Of course, those charts are unavailable to me. I can adjust
the turns ratio of the input link for impedence matching if I knew which
way to go.

Does anyone remember any generalities in this area about the range of
input impedence one would expect to encounter? Is it very low,eg. 10-20
ohms, or perhaps very high, in the thousands of ohms range?

Thanks,
Dennis W5FRS
[email-masked]

------------------------------

Date: Wed, 5 Feb 1997 13:21:59 -0600 (CST)
From: [email-masked] (michael silva)
To: [email-masked]
Subject: Re: 70V PA output transformers
Message-ID: <[email-masked]>

Jeff wrote: 
>
>Hi gang--
>
>I was digging around in my transformer bin last night, and retrieved 
one of
>my several "70V line transformers" which are in fact PA audio output
>transformers.  I've often wondered what it is about the transformer 
that
>makes it a 70V transformer.  Do they use a 70V audio signal to define 
the
>impedence?  Are the primaries of all 70V transformers the same 
impedence,
>then?

Yes and yes, AFAIK.  For example, the 1 Watt tap on a 70.7 transformer 
has a primary impedance of (70.7 * 70.7)/1 or 5000 ohms (with the 
secondary connected to it's design impedance).  Some catalogs actually 
list both primary impedances and wattages, and the relationship as 
described above.

73,
Mike, KK6GM

------------------------------

Date: Wed, 5 Feb 1997 17:14:59 -0500 (EST)
From: [email-masked]
To: [email-masked]
Cc: [email-masked]
Subject: Re: Ancient knowledge; class C grid impedence
Message-ID: <[email-masked]>

> 
> Situation: trying to drive a P-P, class C amp, link coupled input, with an
> exciter designed for 50-70 ohm load.

Should work fine.

I am assuming the input is a tuned tank in the amplifier with a link
and coax to the driver.  If it is anything else, it won't work.
You can install a pinet as the input circuit and that works fine.
It is just the reverse of the traditional transmitter output pinet.

> Problem: appearent impedence mismatch causing "rough" sounding tone on a
> monitoring receiver. Plenty of driving watts available.

Too much or too little driving power can cause that.  If you are using
a sandystate driver, and the link does not match the driver that will
overload them and sometimes generate problems like the rough sounding
notes.   My TS-140S is notorious for that sort of thing.  I have noticed
that underdriving an amplifier due to insufficient grid voltage will
cause it to have a rough sounding note.  I am not exactly sure why,
theoretically.

> Experiment: I coupled the amp to the exciter through a small antenna tuner
> and was able to get good sounding tone. Grid current indicates same DC
> values whether tone is rough or smooth, and output of amp is same also,
> regardless of tone. BTW, I can't tell which direction the antenna tuner
> is transforming the impedence.

The tuner is transforming impedances or tuning the link and/or transforming
impedances both.  This can increase the net grid drive, which would indicate
insufficient grid drive was your problem.

Tight link coupling does not need tuning, but loose link coupling does need
tuning to give the best match.  Normally the link is a series tuned affair
where you have a high C value and a low L value resonant at the desired
frequency.  A 3 turn link needs about 600-1000 pf or so to resonate at
160/80M.  The alternative is to use a full series tuned tuner (a series
coil and capacitor resonant at the desired frequency) and then a small
1/2/3 turn link to couple into the amplifier.  The coil and capacitor
resonate the system and the link then couples into the following amplifier.

>From your design, that you gave at the start, it is not apparent exactly
what the input circuit actually is.  I am making the assumption that it
is a tuned tank with a link coupling.  I would use the series LC antenna
tuner and a 2 or 3 turn link to couple into the amplifier from the driver.
That should handle most requirements.  The better alternative is a pinet
input tuner to the amplifier, as you experimented with for the optimum
and most flexible coupling.

> I refered to the Wm. Orr texts on class C amplifier design and his calcu-
> lations all require detail data from tube curve charts to resolve input
> impedence. Of course, those charts are unavailable to me. I can adjust
> the turns ratio of the input link for impedence matching if I knew which
> way to go.  

Tuning the link coupling system will get around those high-level
charts and calculations.

My rule of thumb is never use a link of greater than three turns.
That usually will match pretty well on my gear for pinet output.
That is what I use on my breadboard antenna tuner as its input from
HW-16 or the AN/SRT-14 pinet.  The link is close-coupled into the
grounded antenna tuner coil.  Works fine for me.

If you use a test setup of 1, 2, or 3 turns, you should easily begin
to see any impedance effect.
 
> Does anyone remember any generalities in this area about the range of
> input impedence one would expect to encounter? Is it very low,eg. 10-20
> ohms, or perhaps very high, in the thousands of ohms range?

The input tank of the amplifer, assuming it has an input tank is high
impedance (several thousands of ohms generically, unless you use swamping
resistors to tame it).  The link is typically low impedance of the range
of 10-50 ohms.

My gut feeling is that you are underdriving the thing with the link
only.  You will most likely need to resonate the link with a series
capacitor or a series coil and capacitor (or the pinet tuner you used)
for best results.

Good LUck!
73/ZUT DE NA4G/Bob

------------------------------

Date: Wed, 5 Feb 1997 15:00:00 -0600 (CST)
From: Dave <[email-masked]>
To: [email-masked]
Subject: 70v Transformers - another question
Message-ID: <[email-masked]>

At 05:19 PM 2/5/97 GMT, you wrote:
>Hi gang--
>
>I was digging around in my transformer bin last night, and retrieved one of
>my several "70V line transformers" which are in fact PA audio output
>transformers.  I've often wondered what it is about the transformer that
>makes it a 70V transformer.  Do they use a 70V audio signal to define the
>impedence?  Are the primaries of all 70V transformers the same impedence,
>then?
>

Thanks for a good question, Jeff.  I'd like to add another
bit:

Is there a glowbug application for them?  I also have some 25v transformers
around as well.  

73's

Dave WB7AWK
* * * * * * * * 

"Sure it's 1939 technology.  But it's GOOD 1939 technology"

------------------------------

Date: Wed, 05 Feb 1997 20:02:37 GMT
From: [email-masked] (Brian Carling G3XLQ/AF4K)
To: [email-masked]
Subject: Re: Radio Swap Meet
Message-ID: <[email-masked]>

I hope this is appropriate & useful to someone on here!
On Wed, 05 Feb 1997 10:27:16 -0800,  this appeared in r.r.s:

|>On May 10th NORTHWEST VINTAGE RADIO SOCIETY & PORTLAND AMATEUR RADIO CLUB 
|>will host a vintage/amateur radio swap meet at the hillsboro armory 
|>{Washington co fairgrounds}Admission will be $2 and swap tables are $10 
|>{includes table & two passes}Overnight RV parking will be $10w/hookup & 
|>$5w/o.You may unload your gear on Friday night & Saturday at 7:am. Doors 
|>will open at 9:am till around 3:pm.There will also be VE testing at 9:am 
|>& 12:noon, you must pre register for the {9:am} session no later than May 
|>3rd.We will also have some refreshments too!! We also have door prizes to 
|>give away.Tables,rv parking must be prepaid by April 25th & confirmation 
|>will be sent to you. For ve testing you must register with Greg 
|>Nightingale KK7GN 360-576-1989 or E-mail [email-masked] For more info 
|>please contact: Kirk Smith KB7EGK 503-786-5142 E-mail 
|>[email-masked] and Myron White 503-629-5513  HOPE TO SEE YA THERE!!

73 from Bry  (((Amateur Radio G3XLQ / AF4K)))
http://www.mnsinc.com/bry/
E-mail:  [email-masked]
Home of MEGALIST ham radio files, SWL info. etc. etc.

------------------------------

Date: Wed, 5 Feb 1997 16:55:34 -0700
From: [email-masked] (Jeff Duntemann)
To: [email-masked]
Cc: [email-masked]
Subject: Re: 70v Transformers - another question
Message-ID: <[email-masked]>

Regarding 70V line transformers, Dave asked:

>Is there a glowbug application for them?  I also have some 25v transformers
>around as well.  

That's almost certain, though it would be helpful to fully understand what
those transformers actually are.  I was looking for a transformer to match
a 2200 ohm source to a 10 ohm load and wondering if I could jigger one of
those 70V jobs to come close.  Then I realized I wasn't entirely confident
what the input impedence to one of those transformers is, though the
consensus here seems to be that the 10W tap gives you 500 ohms.

I have enough information to do the math, I think, and if it works I'll
certainly let people here know.

(The application I'm sketching out on paper is a 12V IF-detector strip
using space charge tubes and a period TO-36 transistor power audio final.
I have the tubes and I have the transistor and I could wire it in an
evening.  I'm not sure what I'd get but because it's a non-lethal tube
circuit it could be useful for sharing with young hands.  Not sure when
I'll have time to build it but failing that transformer I have all the parts.)

--73--

--Jeff Duntemann KG7JF
  Scottsdale, Arizona

------------------------------

Date: Wed, 05 Feb 1997 20:59:56 GMT
From: [email-masked] (Brian Carling G3XLQ/AF4K)
To: [email-masked]
Subject: Re: 624 Kits / a source of rocks
Message-ID: <[email-masked]>

Pat Bunn  N4LTA has been selling QRP transmitter kits for years
and looks like he is going slowly out of business.
What he may have that will interest GB aficionados is a
supply of crystals for the ham CW bands!

May I suggest that you e-mail him if you need some.
Maybe he will make us a group deal on them????

From: [email-masked] (Pat Bunn)
Date: 4 Feb 1997 18:50:35 GMT

As most of you have heard , 624 Kits is no longer in business except for 
offering the 100 watt output 6 meter amplifier and a 6 meter receive 
converter.

I have a very large amount of leftover parts, PC Boards, crystals
toroids ect that I wish to rid myself of. If you are interested as a 
club or individual please Email me for a list.

Pat Bunn, N4LTA

73 from Bry  (((Amateur Radio G3XLQ / AF4K)))
http://www.mnsinc.com/bry/
E-mail:  [email-masked]  *** REMOVE ".NO_SPAM" to reply ***
Home of MEGALIST ham radio files, SWL info. etc. etc.

------------------------------

Date: 	Wed, 5 Feb 1997 15:12:01 -1000
From: Jeffrey Herman <[email-masked]>
To: Glowbugs List <[email-masked]>
Subject: Even more thoughts re: 1843.2 kc
Message-ID: <Pine.GSO.3.93.970205150818.24125A-100000@uhunix3>

Here are a few more comments from the guys on 160m mail list regarding
the use of 1843.2 kc for AM QRP. This will be the last batch that I'll
forward (I think you all get the idea!).
73,
Jeff KH2PZ
-----------------------------------------------------------------------

     Hi Jeff, 
     Here are my thoughts:
     If the guys are using truly 5 watt or less AM radios and are using a 
     marginal antenna, they will be less problem than the fish nets.  
     Otherwise, they could be a problem when the band is open and European 
     SSB is coming through.  The national QRP calling frequency is 1910 in 
     the middle of the JA window!!  I would guess 1895 would be a lot 
     safer, and they would not get blown away by KWs and contesters.
     73         George          K8GG

Dear Jeff,
1843 is prime DX territory, according to both actual use and band plan.
Although QRP might not bother too many people over a broad area, AM uses a lot
of bandwidth and anyone local would almost certainly object.  It doesn't take
much of a signal to wipe out a DX station from across the globe.  
Judging from what I see on the band, with a lot of SSB ragchew between 1850 and
1900, and the JA window from 1907.5 to 1912.5, the best spot for AM of any kind
would be 1925 or up.  I imagine with QRP, one doesn't want to fight much QRM, so
staying in the less populated part of the band would have an advantage.
I think the price of a crystal would be cheaper than the hassle of trying to run
on 1843, unless the objective is to scrounge absolutely everything needed to
make these rigs.  In that case, I think there are probably some articles in QST
or other mags on grinding crystals to other frequencies.  
A VFO is pretty easy to make to run on 160, and is not really much more
complicated than a crystal oscillator, since no mixing would be necessary.
What is the address of the GlowBugs?  I run tubes myself and am interested in
building stuff around some old tubes my Grandfather has.
73 and good luck, Rob K2WI

I assume you have a whole bunch of mail by now with people telling
you this part of the band is highly used for international SSB
QSOs!  So, here is another one.
Just two nights ago, I worked D44BC on 1843 kHz.  Most DX I hear
on SSB is between 1840 and 1847, which would pretty much be filled
with an AM signal.
Doesn't sound like it would work out too well.
73 Tree N6TR

Hi Jeff...well as both a Firebottle Nut and a 160 Mtr DX nut!! I will 
have to say that if you fire up on 1843.2 kc with a AM radio or even 
a SSB radio and you are not looking for or working DX you will be 
chastized severely.........need to get up above 1925 kc to do AM!!
de John K9UWA / P40WA
                  Top Band Forever
                  160 DXCC  250 / 245
                  160 WAZ   40 / 40

Jeff, I can't see a problem.  The freq. is above the DX window and below
most of the phone operation.
Good DX
73, Brad

        Jeff, 1843 is in the 160 meter ssb portion on the band.
1800 to 1830 is cw, 1830 to 1840 is dx window, 1840 up ssb and ssb dx.
you can operate cw on 1843, but probably be real rough with kw ssb
stations there.  Or you can operate AM there, same problem.  
Just my .02 cents worth thanks 73 Merv K9FD

------------------------------

Date: Thu, 6 Feb 1997 04:52:14 +0000
From: "Brian Carling" <[email-masked]>
To: [email-masked]
Subject: Re: Top Band Frequency
Message-ID: <[email-masked]>

On  5 Feb 97  Re: 1832 kc.
BA BOB says:

> The problem is that that is smack in the middle of a lot of fone
> activity.  They get pretty testy when cw folks creep up that far.
> If a tiny AM did likewyse, dunno.  They might freak out or be happy.

> 73/ZUT DE NA4G/Bob UP

I think it would NOT be a problem for AM at that FREQ. You see,
AM and SSB co-exist just fine on 75m around 3880 kc.

Of course, there is some QRM but you expect that with phone, and atl 
least the SSB boys can hear the AM exalted carrier mode.

Now, if we are running QRP AM also, I think the biggest problem may 
be hearing each other!

Anyone game for a 100-200 watt plate modulated project on 1832? 

I think if someone would help me find modulation transformers I would 
go for it in a heartbeat!

SO far, I have not had much luck finding any.

********************************************************
*** 73 from Radio AF4K / G3XLQ in Gaithersburg, MD USA *
**  E-mail to:  [email-masked]                         *
*** See the great ham radio resources at:              *
**  http://www.mnsinc.com/bry/                         *
********************************************************

------------------------------

Date: Thu, 6 Feb 97 09:13:27 EST
From: [email-masked] (John Heck)
To: [email-masked]
Subject: Tube base removal
Message-ID: <[email-masked]>

Folks,
How does one go about cleanly removing the bases from tubes? I have a buncha 
duds whose bases I would like to use for coil forms. I have read that you can
boil the tubes to loosen the base from the bulb, but how do you unsolder the
pins all at once to remove the bulb without damaging the base? Thank you.

Regards,
John Heck, KC8ETS
1009 Donson Drive
Dayton, Ohio 45429
(513)865-7036(work)
[email-masked]

------------------------------

Date: Thu, 06 Feb 97 08:38:48 cst
From: [email-masked]
To: [email-masked], [email-masked]
Subject: Re[2]: Top Band Frequency
Message-ID: <[email-masked]>

Hey Y'all:
        We also coexist on 7290.  There is a group up in the Ohio area 
that is on about 1300 EST while my buddy WB5NMH and I are on 7290 USB. 
We don't seem to bother them and they don't bother us.  It's great 
that we can share the frequency at the same time.  Indeed there is 
activity on 7290 LSB at the same time we are on USB!  How's that for 
cooperation?

        Actually, I had a 100 to 200 Watt plate modulated rig in mind 
when I made my original query.  I haven't tried to find a modulation 
transformer yet, but I figure that I could at least get something 
going using a FET for series modulation until I can find a suitable 
transformer.  I figure 1000V for a plate supply for the peaks and 500V 
for unmodulated carrier feeding a couple of 6146B's.  When I get the 
modulation transformer I can boost the plate voltage up to 750 V.

        From Jeff's post, we might want to find another frequency for 
AM activity, since it is in the DX window.  Looks like the VFO is the 
way to go.  It's a shame.  My oscillators usually don't and my 
amplifiers usually do :<)

Ray Mack
WD5IFS
[email-masked]
Friendswood (Houston), TX

______________________________ Reply Separator _________________________________
Subject: Re: Top Band Frequency
<snip>
I think it would NOT be a problem for AM at that FREQ. You see, 
AM and SSB co-exist just fine on 75m around 3880 kc.
<snip>
Anyone game for a 100-200 watt plate modulated project on 1832? 

I think if someone would help me find modulation transformers I would 
go for it in a heartbeat!

SO far, I have not had much luck finding any.

******************************************************** 
*** 73 from Radio AF4K / G3XLQ in Gaithersburg, MD USA * 
**  E-mail to:  [email-masked]                         * 
*** See the great ham radio resources at:              * 
**  http://www.mnsinc.com/bry/                         * 
********************************************************

------------------------------

Date: Thu, 6 Feb 1997 08:12:09 -0700
From: [email-masked] (Jeff Duntemann)
To: [email-masked]
Cc: [email-masked]
Subject: Re: Tube base removal
Message-ID: <[email-masked]>

At 02:13 PM 2/6/97 GMT, KC8ETS wrote:
>Folks,
>How does one go about cleanly removing the bases from tubes? I have a buncha 
>duds whose bases I would like to use for coil forms. I have read that you can
>boil the tubes to loosen the base from the bulb, but how do you unsolder the
>pins all at once to remove the bulb without damaging the base? Thank you.

First of all, choose your battles.  Wiggle the bases on all your duds to
see if any are the least bit loose.  If the envelope has let go of the
base, it's a snap, especially on those wonderful old G bottles:

Grip the glass envelope between the ball of your left hand (vise versa if
you're a southpaw) and your little finger, with the base up.  Take your
soldering iron and heat as many of the pins simultaneously as the geometry
of the tip will allow.  With the fingers of your left hand, rock the base
*away* from the envelope on the side your heating, so that the wires will
be pulled back out of the base a little.  When you can't go any further
that way, rotate the tube 90 degrees and heat the next two or three pins,
rocking the base so that when the pin solder loosens the wire will be
pulled down out of the base.  Couple times around and it comes out clean.

This sounds couplex, but it's really pretty simple and I've done it
numerous times.

I've never tried to loosen the adhesive holding the tube envelope to the
base, but boiling would be something to try.  Too much water exposure can
damage some phenolics, tho--tubes were not meant to get wet, and I'd be
careful here.  On the other hand, they're duds, right?

I'm not sure if they still offer them, but AES used to sell *unused* octal
tube bases for a buck apiece; I bought a dozen.

Something you guys should probably not bother trying: Grinding the top off
a dead 12AX7 on a diamond wheel, surgically removing its innards, and then
winding small coils on it, soldering the leads to the pins on the bottom
without trying to go inside the envelope.  Did this once.  Won't do it again.

--73--

--Jeff Duntemann KG7JF
  Scottsdale, Arizona

------------------------------

Date: Thu, 06 Feb 1997 09:48:11 -0500
From: Roy Morgan <[email-masked]>
To: [email-masked]
Subject: Re: 70V PA output transformers
Message-ID: <[email-masked]>

At 07:22 PM 2/5/97 GMT, you wrote:
>Jeff wrote: 
>>
>>Hi gang--
>>
>>I was digging around ...  several "70V line transformers"  

 ...   Do they use a 70V audio signal to define the
>>impedence?  Are the primaries of all 70V transformers the same 
>impedence, then?

A little more on this:

 - Public address system and theater system engineers adopted 70 volts as a
compromise between avoiding electrical wiring code requirements and
efficiency of audio power distribution (according to a Western Electric
brochure I have).

 - The distribution line will have 70 volts rms on it when the amplifier is
delivering its full rated power (whatever that happens to be).

 - The loads attached to the line should add up to the full rated power of
the amplifier.  (If they don't, the amp will see a load impedance NOT what
it was designed for, with attendant distortion and other problems).

 - The chosen tap on each line transformer will deliver to its load the
power indicated on that tap with 70 volts on the line.  That is, the input
impedance of that tap is such that at 70vrms, it will dissipate the
indicated power.

 - In distribution systems, highest fi is usually not important, but best
results will occur when transformers are operated at or very near their
design impedances.  A few minutes with your slide rule will get you the
input impedances (sorry, I can't find the table I've saved).

These tranformers are just the thing for getting speaker power out of such
receivers as the R-390 and the vernerable RAL and RAK.  No glowbuggers
shack should be without one.

If you drive 'em with toobes, they sound better.

Keep em glowing!

-- Roy Morgan/Building 820, Room 562/Gaithersburg  MD 20899
(National Institute of Standards and Technology)
301-975-3254 Fax: 301-948-6213  [email-masked] --

------------------------------

Date: Thu, 6 Feb 1997 08:14:06 -0700
From: [email-masked] (Jeff Duntemann)
To: [email-masked]
Cc: [email-masked]
Subject: Re: Re[2]: Top Band Frequency
Message-ID: <[email-masked]>

Ray--

I'd be interested in knowing how to use a FET to series modulate a tube.
Any articles or book citations you could give us?  Or is this "native wisdom?"

--73--

--Jeff Duntemann KG7JF
  Scottsdale, Arizona

>Actually, I had a 100 to 200 Watt plate modulated rig in mind 
>when I made my original query.  I haven't tried to find a modulation 
>transformer yet, but I figure that I could at least get something 
>going using a FET for series modulation until I can find a suitable 
>transformer.  I figure 1000V for a plate supply for the peaks and 500V 
>for unmodulated carrier feeding a couple of 6146B's.  When I get the 
>modulation transformer I can boost the plate voltage up to 750 V.

------------------------------

Date: Thu, 06 Feb 1997 10:34:48 -0500
From: Roy Morgan <[email-masked]>
To: [email-masked]
Subject: Re: Tube base removal
Message-ID: <[email-masked]>

At 02:13 PM 2/6/97 GMT, you wrote:
>Folks,
>How does one go about cleanly removing the bases from tubes? I have a buncha 
>duds whose bases I would like to use for coil forms. I have read that you can
>boil the tubes to loosen the base from the bulb,

UNlikely!  

May I quote from "An Excerpt from TUBE LORE, A reference for Users and
Collectors" by Ludwell Sibley, Sound Practices Number 12:

"Solvents (acetone, etc.) are ineffective in softening the old base cement
- the cement was baked hard in manufacture, and "nothing" dissolves it."

My method is to wrap the tube in a rag, smash with hammer, then de-gut the
base with pliars and utility knife.  Unsolder pin leads one at a time after
the glass is broken out.

 ...    but how do you unsolder the
>pins all at once to remove the bulb without damaging the base? 

If the base is loose already, twisting may break the leads.  If it doesn't
fasten the base in a vice or other clamp, wave the bernzomatic torch over
it, and wiggle the tube.  The leads are usually soldered only at the very
tip, and need only a little heat to loosen.

-- Roy Morgan/Building 820, Room 562/Gaithersburg  MD 20899
(National Institute of Standards and Technology)
301-975-3254 Fax: 301-948-6213  [email-masked] --

------------------------------

Date: 06 Feb 1997 10:04:10 CST
From: "KASTIGAR, MATTHEW (M" <[email-masked]>
To: [email-masked]
Subject: R-392 assistance!
Message-ID: <[email-masked]>

Microsoft Mail v3.0 IPM.Microsoft Mail.Note
From: KASTIGAR, MATTHEW (MM)
To:  'internet@swgate1'
Subject:  R-392 assistance!
Date: 1997-02-06 10:07
Priority:
Message ID: 9392B2E2
Conversation ID: 9392B2E2

------------------------------------------------------------------------------

internet: [email-masked]

Help!
I have an R-392 (vehicular version of the R-390, I understand) and it has
been partially disassembled (!)... It appears to have all of the parts, but
I would like a copy of the manual for reference.  Luckily, the tuning parts
(cams, gears) is intact, only the 'outer' parts and screws removed.
     *ANY* help appreciated!
THX,
Matt N0XEU
[email-masked]

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Date: Thu, 06 Feb 97 10:36:09 cst
From: [email-masked]
To: [email-masked]
Subject: Re[4]: Top Band Frequency
Message-ID: <[email-masked]>

Hey Y'all:
        I guess this falls under "native wisdom" since I am a hardware 
design engineer by training.  The way I plan to do it is just like the 
linear regulator stuff you see in the Handbook for doing 12 VDC 
supplies.  Instead of a DC reference, I will put my audio signal  into 
the refence input.  There are a lot of cheap FET's around that will 
handle 1000 VDC these days.  Probably, to be safe, I'll set the plate 
supply to 800VDC max and use a couple of IRFPG30 FET's from DigiKey.  
They are $12 each and are rated at 1000VDC, 3 A max, @ 125W.  The 
IRFG20 is a similar transistor, but it is in the TO220 package vs 
TO247AA.  It is only $6.48, but it is only good for 54W.

        This approach is *definately* brute force.  I'll need a mondo 
heat sink and lots of air to dissipate the 100W or so of continuous 
dissipation with no modulation.  This is where a class AB modulator 
really shines.  The only time you dissipate full power in the system 
is on voice peaks.  Normally you only have the waste power in the 
finals themselves.  With the series system, the total power from the 
power transformer remains the same.

Ray Mack
WD5IFS
[email-masked]
Friendswood (Houston), TX
______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: Top Band Frequency
Author:  [email-masked] at mails
Date:    2/6/97 9:17 AM

Ray--

I'd be interested in knowing how to use a FET to series modulate a tube.
Any articles or book citations you could give us?  Or is this "native wisdom?"

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Date: Thu, 6 Feb 1997 11:01:57 -0600
From: [email-masked] (William H. Launer)
To: [email-masked]
Subject: Re: Tube base removal
Message-ID: <v01530500af1fb5a83d41@[192.0.2.1]>

If it's a "dud" tube, and I just want the base, I use the old "hammer
and paper bag" routine.  The bag retains the broken glass, and other
"nasties" from the broken tube.  Then unsolder the wires one at a time.

73, Bill wb0cld

Bill Launer
St. Charles, MO
[email-masked]
[email-masked] [44.46.66.25]
qrp-l #279      qrp arci #3551
Grid Square EM48RT

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Date: Thu, 6 Feb 1997 11:18:54 -0600
From: [email-masked] (William Hawkins)
To: [email-masked]
Subject: Audio impedance matching
Message-ID: <[email-masked]>

Audio impedance matching is really concerned with preventing overload.

When a speaker is rated at 4 ohms impedance, that's the worst case value,
that occurs at resonance and is about the DC resistance of the voice coil
(unless you've got crossover networks and other speakers). The impedance
increases dramatically as you move away from resonance, and is affected
my more things than most folks would care to measure.  It's unpredictable.

The amplifier has negative feedback.  It faithfully (more or less)
reproduces the input voltage waveform at the output from zero load
(infinite impedance) up to the point where the power tubes can't
control enough power to keep the voltage up.  Then you get clipping
and distortion and all those things the golden ear crowd loves.

So a public address distribution amplifier is designed for maximum power
transfer at 70 volts output. You tack on transformers that tell you how
much power you will draw at 70 volts with a selected secondary impedance.
You add them all up and stop at the amplifier power rating (or say what
the heck, nobody listens at resonance anyway, and double it).

Not at all like RF impedance matching, eh?

Regards,
Bill Hawkins  [email-masked]

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Date: Thu, 6 Feb 1997 17:09:03 +0200
From: [email-masked] (Wouter de Waal)
To: [email-masked]
Subject: Re: Tube base removal
Message-ID: <[email-masked]>

>Folks,
>How does one go about cleanly removing the bases from tubes? I have a buncha 
>duds whose bases I would like to use for coil forms. I have read that you can
>boil the tubes to loosen the base from the bulb, but how do you unsolder the
>pins all at once to remove the bulb without damaging the base? Thank you.

Use a hammer. Really. You didn't want to keep the glass in one piece did you?

W

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End of GLOWBUGS Digest 438
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