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6SN7 push pull flea amplifier project
6SN7 push pull flea amplifier project
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Old 18th February 2017, 07:29 AM   #21
Shoog is offline Shoog
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I can attest that garter bias is a great system for biasing up an amp like this. I build a PL82 PP amp with garter bias and it sounds great.
However 6AS7 project its going to be very wasteful. I suggest digging into the Tubecad articles a bit deeper because he showed another garter bias arrangement which used transistors which saved a lot on the voltage overhead. I built a 5687 preamp with wilson current mirrors for equal bias on both sides, and the tubcad article I mentioned is a hybrid of pure garter and current mirror.

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Old 18th February 2017, 07:57 AM   #22
SemperFi is offline SemperFi  Wake Island
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Cool project. I have a similar 5687 based flea amp in the office.
What is 'garter' bias?
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Old 18th February 2017, 09:57 AM   #23
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Here is the only article on garter bias and it covers the transistor variant.

Blumlein’s Garter Circuit Revisited

What power do you get out of your 5687 flea.

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Old 18th February 2017, 12:57 PM   #24
Lingwendil is offline Lingwendil  United States
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6SN7 push pull flea amplifier project
Quote:
Originally Posted by Shoog View Post
Here is the only article on garter bias and it covers the transistor variant.

Blumlein’s Garter Circuit Revisited

What power do you get out of your 5687 flea.

Shoog
Only article eh

Amplifier auto bias circuits: Alan Dower Blumlein's garter circuit

Interestingly, I can't find much reference to garter bias, other than mentions that he wasn't the first to do it, I have a similar patent printed out somewhere but forget the number and author. The patented version has additional components however, so is not exactly similar.

EDIT- Murray John Somerset
Patent US3127569 - Valve amplifier push-pull output stage - Google Patents

Last edited by Lingwendil; 18th February 2017 at 01:06 PM.
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Old 18th February 2017, 02:56 PM   #25
SemperFi is offline SemperFi  Wake Island
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Quote:
Originally Posted by Shoog View Post
Here is the only article on garter bias and it covers the transistor variant.

Blumlein’s Garter Circuit Revisited

What power do you get out of your 5687 flea.

Shoog
Very little. Less than 1watt. That was another one of those 'use the parts in the bin' project and the b+ is a lousy 200volts. I have also built this pse with 3 5687 and one 6922 per ch.
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Old 19th February 2017, 12:17 AM   #26
Lingwendil is offline Lingwendil  United States
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6SN7 push pull flea amplifier project


That's effin' rad dude! Gives me ideas for parallel push pull designs now! Six bottles per side for a fancy V12 amp with something like EL84 or 6V6 would be sweet, and I just so happen to have a dozen of each on hand if I'm not mistaken...

Got a schematic?


Bidding on some tubes on eBay to hopefully get a few pairs of some GTA types for the higher voltage version of this flea design, maybe even some goofy coin-base tubes...

Last edited by Lingwendil; 19th February 2017 at 12:33 AM.
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Old 19th February 2017, 10:50 AM   #27
SemperFi is offline SemperFi  Wake Island
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Thanks. My next engine will use tubes with top cap. I also have drawn up a 45degree V2 with 813s. Harley music engine.
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Old 19th February 2017, 09:33 PM   #28
Sodacose is offline Sodacose  United States
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Quote:
Originally Posted by Lingwendil View Post
For anybody wondering, this would make a killer headphone amplifier, especially for power hungry 16-32 ohm headphones...
You got me pegged I recently designed a little differential headphone amp (5687 or ECC99 output tubes) but I've wondered about how a 6SN7 might behave in a similar arrangement. The issue was finding a transformer that will keep them happy (pretty high turns ratio needed for the 6k Rp).
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Old 19th February 2017, 09:41 PM   #29
Lingwendil is offline Lingwendil  United States
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6SN7 push pull flea amplifier project
Grab a transformer that you would usually use for an EL84 or 6V6 (from 8k~10k) push-pull, and run twice the nominal load impedance on the taps (examples- 8 ohms on a 4 ohm tap, 16 ohms on an 8 ohm tap, 32 ohms on an 8 ohm tap) to give anywhere from 16-20k load, and it should work well. For such low power 70 volt PA line transformers work well too, as long as they have the correct taps. I have a few line trannies from Atlas Sound that work great for this purpose. Or, be a loon like Shoog and me and play with power toroids
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Old 19th February 2017, 10:50 PM   #30
Sodacose is offline Sodacose  United States
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Yeah, after responding I realized that 8k:4 ohm would actually be about right for 6SN7 push pull. The ECC99/5687 amp I mentioned used an 8k:8 ohm Edcor for 8k per tube with a 32 ohm headphone load. Too bad most Edcors don't have the multiple taps.
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