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John L Stewart John L Stewart is offline
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Location: Toronto
Posts: 301
Default Small Fully Integrated Amplifier

This is something I built in 1968. Finally wrote it up in 2005. Go to-

www.audioXpress.com

& click on the tab Web-exclusive Articles.

There you will find the PDF 'A Tiny Vintage Garage Amp'.

Ya, I know, you could do better!!

Cheers to all, John
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Patrick Turner Patrick Turner is offline
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Default Small Fully Integrated Amplifier

On Mar 11, 2:27*am, John L Stewart John.L.Stewart.
wrote:
This is something I built in 1968. Finally wrote it up in 2005. Go to-

www.audioXpress.com

& click on the tab Web-exclusive Articles.

There you will find the PDF 'A Tiny Vintage Garage Amp'.

Ya, I know, you could do better!!

Cheers to all, John

--
John L Stewart


Not bad John and its like many guitar practice amps. The 6AQ5 is
harder to find now than EL84 which probably has a mushier over drive
sound than 6AQ6. Maybe consider adding variable NFB. And where's the
reverb tank and speaker?
Golden Tone amps in Oz used to make a guitar amp with a single EL84 in
the 1960s, but no reverb, but with 12" speaker.
Because its PT was more than large enough I was able to change it tp
PP with two 6V6. It had a very primitve and thumpy going tremelo, so I
put in tremolo from Fender with neon and LDR under wrap, much better.
Not much NFB used, THD below clipp don't matter, sounded OK for small
venues or practice. Lat week I repaired another Golden Tone PP with PP
6AQ5. No FB at all. Input was 6AU6 in pentode, high gain, and power
amp driver was 12AX7, one input gain, one concertina inverter. Tone
was controlled by a cap and pot from the first audio gain 12AX7 to
ground. The rising speaker impedance without NFB ensures a bright
sound, and this can be cut with the tone cut control. No need to boost
bass, just cut treble and turn up volume. Not much deep bass anyhow
because the cabinet is small, 6mm plywood. and the back panel has long
been lost.

There were two inputs feeding together for the input 6AU6 so a singer
and piano-accordian could liven up an Italian wedding. Sound quality
was controlled by red wine. But Geloso made a special little baby amp
head for which a speaker in box was needed.
http://www.flickr.com/photos/25988513@N08/2504502894/

I rescued one at a rubbish tip in 1994, moments before a bulldozer ran
over it. I repaired the arcing OPT and rewired it and sold it for $350
to a bloke who had another and they much suited his music classes at
the school where he taught. He's now Dr Zot. http://www.zot.com.au/vintage..html

Patrick Turner.
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John L Stewart John L Stewart is offline
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Location: Toronto
Posts: 301
Default

Quote:
Originally Posted by Patrick Turner View Post
On Mar 11, 2:27*am, John L Stewart John.L.Stewart.
wrote:
This is something I built in 1968. Finally wrote it up in 2005. Go to-

www.audioXpress.com

& click on the tab Web-exclusive Articles.

There you will find the PDF 'A Tiny Vintage Garage Amp'.

Ya, I know, you could do better!!

Cheers to all, John

--
John L Stewart


Not bad John and its like many guitar practice amps. The 6AQ5 is
harder to find now than EL84 which probably has a mushier over drive
sound than 6AQ6. Maybe consider adding variable NFB. And where's the
reverb tank and speaker?
Golden Tone amps in Oz used to make a guitar amp with a single EL84 in
the 1960s, but no reverb, but with 12" speaker.
Because its PT was more than large enough I was able to change it tp
PP with two 6V6. It had a very primitve and thumpy going tremelo, so I
put in tremolo from Fender with neon and LDR under wrap, much better.
Not much NFB used, THD below clipp don't matter, sounded OK for small
venues or practice. Lat week I repaired another Golden Tone PP with PP
6AQ5. No FB at all. Input was 6AU6 in pentode, high gain, and power
amp driver was 12AX7, one input gain, one concertina inverter. Tone
was controlled by a cap and pot from the first audio gain 12AX7 to
ground. The rising speaker impedance without NFB ensures a bright
sound, and this can be cut with the tone cut control. No need to boost
bass, just cut treble and turn up volume. Not much deep bass anyhow
because the cabinet is small, 6mm plywood. and the back panel has long
been lost.

There were two inputs feeding together for the input 6AU6 so a singer
and piano-accordian could liven up an Italian wedding. Sound quality
was controlled by red wine. But Geloso made a special little baby amp
head for which a speaker in box was needed.
http://www.flickr.com/photos/25988513@N08/2504502894/

I rescued one at a rubbish tip in 1994, moments before a bulldozer ran
over it. I repaired the arcing OPT and rewired it and sold it for $350
to a bloke who had another and they much suited his music classes at
the school where he taught. He's now Dr Zot. http://www.zot.com.au/vintage..html

Patrick Turner.
Anyway, not a guitar amp but I guess it could be used for a bit of practice. But not by me, I've finally got as far as learning how to play the radio. This amp has been running in various parts of the house since it was built. Running now in the workshop. Built in a 8x12x3 chassis, so no room for a tank.

Did an amp many years ago with +ve current FB from the OPT Secondary. Used a piece of resistance wire to pickoff the current sample. Interesting to watch the scope while driving the resonance of the speaker load as the +FB was varied. Too much & then instabilty. But once setup with the users speaker it worked well for years.

For a very complete compendium of guitar amp schematics try The Tube Amp Book, 4th Edition by Aspen Pitman. A very good resource indeed. Besides the schemas there are lots of photos. My copy is about 10 years old. The editors keep adding to it so it may be into the 5th Edition.

Objectives & circuitry usually not hifi. Not what the users want.

Oddly, The McIntosh schema is included. I think Pitman referes to it as the 'King of Tube Amps'. I would have to agree with that. And the Williamson schema is shown as a late entry.

Cheers, John
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John L Stewart John L Stewart is offline
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Location: Toronto
Posts: 301
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Quote:
Originally Posted by flipper View Post
On Thu, 10 Mar 2011 15:27:03 +0000, John L Stewart
wrote:


This is something I built in 1968. Finally wrote it up in 2005. Go to-

www.audioXpress.com

& click on the tab Web-exclusive Articles.

There you will find the PDF 'A Tiny Vintage Garage Amp'.

Ya, I know, you could do better!!

Cheers to all, John


Nice little amp you got there.

My 'simple 3W' SE is even simpler because it's made with 'modern
times' in mind, PCs in particular, so the preamp and tone controls are
in the computer. The OPTs are some inexpensive 2k jobs from Radiodaze.
The isolation transformer is only 11 bucks from Mouser and 'more
power' than needed so I took advantage of that for DC heaters.

http://flipperhome.dyndns.org/Tin%20Man.htm

My PP version uses 6AW8s and low cost line transformers.

http://flipperhome.dyndns.org/6AW8PCSpkr.htm

I gave Tin Man to my brother in law but use the 6AW8 amp here all the
time.

A beefier 'TV tube' amp went to my sister.

http://flipperhome.dyndns.org/13FD7%...Williamson.htm

The 13FD7 is a 9 pin 13EM7 and I think they look pretty darn good as
long as you turn the side getter flash to the back.
-------------------------------------------

Hey Flipper, I like your use of low cost tubes that few can figure out an application for such as your 45B5s & the 20EZ7. And the pie tins are a nice touch.

Used to think about using pie tins but the way things are going they may be no longer available. And they if are, will the thin metal be still strong enough?

You reminded me of a guy in Texas who built amplifiers commercially back about 15 years ago, name of Alvin Bryant. He was written up by Joe Roberts of the now definct magazine Sound Practices. Al favoured PP 300Bs & lots of iron. He was a chain smoker & I think now quite dead. But I guess he had a lot of fun anyway!

I did buy a couple of 6AW8s a few years ago for my stash, figuring to try a low power amp as you have. Yours looks great, nice to see it can be done.

I did a couple of projects similar to your 13EM7 a few years ago for publication in AudioXpress magazine. The first was a 6EA7/6EM7 connected as a FB pair & got very good results.

The next was simply a 6LU8, again a FB pair on the same chassis as above by changing the socket. That way it could run SET or by a simple reconnexion run SEUL. Both results very good. I document all my stuff as proof, unlike a lot of the stuff that gets published.

I tried that amp as a FB pair, pentode connected. The 6LU8 pentode connected is not a great audio tube at all. Never meant to be but interesting just the same. Modified several 40s radios to FB pairs as well.

Audio is not my main thing. Rather hitech sales. Been with HP, R&S, Field Aviation, Etc. Before that U of T Physics Research & Ferranti Packard 3-phase power station transformers.

It has all been great fun!

Cheers, John
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John L Stewart John L Stewart is offline
Senior Member
 
Location: Toronto
Posts: 301
Default

Quote:
Originally Posted by flipper View Post
On Thu, 10 Mar 2011 15:27:03 +0000, John L Stewart
wrote:


This is something I built in 1968. Finally wrote it up in 2005. Go to-

www.audioXpress.com

& click on the tab Web-exclusive Articles.

There you will find the PDF 'A Tiny Vintage Garage Amp'.

Ya, I know, you could do better!!

Cheers to all, John


Nice little amp you got there.

My 'simple 3W' SE is even simpler because it's made with 'modern
times' in mind, PCs in particular, so the preamp and tone controls are
in the computer. The OPTs are some inexpensive 2k jobs from Radiodaze.
The isolation transformer is only 11 bucks from Mouser and 'more
power' than needed so I took advantage of that for DC heaters.

http://flipperhome.dyndns.org/Tin%20Man.htm

My PP version uses 6AW8s and low cost line transformers.

http://flipperhome.dyndns.org/6AW8PCSpkr.htm

I gave Tin Man to my brother in law but use the 6AW8 amp here all the
time.

A beefier 'TV tube' amp went to my sister.

http://flipperhome.dyndns.org/13FD7%...Williamson.htm

The 13FD7 is a 9 pin 13EM7 and I think they look pretty darn good as
long as you turn the side getter flash to the back.
Hi Flipper- My reference to Alvin Bryant of Texas was meant to indicate that he made extensive use of cake tins as the basis of his amplifiers. Managed to leave that out of the post.

My wife tells me they are still available here, so next time at that store I will take a look. Should be OK for experimental work.

What drawing software are you using? Looks like good stuff.

Cheers, John


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Vance_Iam Vance_Iam is offline
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Quote:
Originally Posted by John L Stewart View Post
This is something I built in 1968. Finally wrote it up in 2005. Go to-

www.audioXpress.com

& click on the tab Web-exclusive Articles.

There you will find the PDF 'A Tiny Vintage Garage Amp'.

Ya, I know, you could do better!!

Cheers to all, John
Thanx for providing information...I'll visit and hope that it will be quite informative. thanks again

Oldies Music

Last edited by Vance_Iam : April 4th 11 at 04:19 PM
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