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First stereo tube amp build advice
First stereo tube amp build advice
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Old 13th November 2020, 09:24 PM   #11
Tom Kamphuys is offline Tom Kamphuys  Netherlands
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Quote:
Originally Posted by painted View Post
My suggestion is to start with a proven concept, like an EL84 push pull. Choose your speakers with easy crossovers, big caps suck the life out of the scarce 2x 12W/ch. A 30W/ch EL34 push pull might come next. If you are brave try a proven SE design, 300B is popular for 8W/ch.
Do you have some examples of these proven concepts?
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Old 13th November 2020, 11:41 PM   #12
6A3sUMMER is offline 6A3sUMMER  United States
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Keep in mind that Tom wants the cost of the amplifier to be no more than 200 Euros.

Some of you in Europe know what kind of low cost power and output transformers are available.

It might be less expensive to purchase a push pull output transformer and two EL84 per channel,
instead of purchasing a much larger single ended output transformer (for equal bass response) and one EL84 per channel.

Or, if Tom wants to do it that way, build a mono-block amp this year, and build a second mono-block amp next year, for example, when budget permits.

Last edited by 6A3sUMMER; 13th November 2020 at 11:46 PM.
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Old 14th November 2020, 12:08 AM   #13
OldHector is offline OldHector  Sweden
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You can get two top quality output transformers and a power transformer for a PCL86 push pull amplifier for €200 ...
toroidy.pl TTG-ECL86PP-Tube-output-transformer-10kOhm-2xECL86-2xPCL86-Push-pull-or-similar

The tubes can be had for €20, then if you search out ECL86 and Dissident Audio, then you have a fine amplifier.

At the other end of the scale, a pair of 112v twin primary toroidal with 9v secondaries would make adequate OPTs for a push pull project, and keep total cost under €200.

Or take it even further. There is still a lot of cheap tube powered gear to be had. I picked up an old Panasonic amp from the 60’s for €100, and it will make a fine integrated amp with 6AR5 outputs.

If you monitor the local auction sites, and then it does not have to be prohibitively expensive to produce something of reasonable quality.
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Old 14th November 2020, 05:05 AM   #14
Tom Kamphuys is offline Tom Kamphuys  Netherlands
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I am willing to spend some more. I probably was too vague. Let's say up to €400-500.
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Old 14th November 2020, 10:37 AM   #15
Eli Duttman is offline Eli Duttman  United States
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€400-500 is quite sufficient to complete an approx. 15 WPC push/pull amp based on "12" W. tubes, like the EL84 and 6V6. Mate the amp to low 90s sensitive speakers and the music will flow.

BTW, a well executed "full wave" voltage doubler is the economical way to obtain a high performance B+ PSU. Good sized caps. in the stack followed by a LC section reservoir get the job done, well. Hint: Hegeman, Marantz, and McIntosh used the method.
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Old 14th November 2020, 12:38 PM   #16
Eli Duttman is offline Eli Duttman  United States
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Tom,

This affordable O/P transformer
(approx. €50) is "perfect" for "12" W. multi-grid "finals".
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Old 15th November 2020, 04:37 PM   #17
Tom Kamphuys is offline Tom Kamphuys  Netherlands
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Thanks for the output transformer links. I've added them to my list of interesting suppliers.

What is the reason choosing PP? Is (was) it the budget? The music I'd like to listen to? The room size?

And I'm still searching for schematics of good simple amps, preferably with some explanation. The schematics I do find look different from the guitar amps I'm used to. Other tricks, other tubes. Is there a book you guys can recommend?
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Old 15th November 2020, 04:41 PM   #18
Tom Kamphuys is offline Tom Kamphuys  Netherlands
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Quote:
Originally Posted by Eli Duttman View Post
€400-500 is quite sufficient to complete an approx. 15 WPC push/pull amp based on "12" W. tubes, like the EL84 and 6V6. Mate the amp to low 90s sensitive speakers and the music will flow.

BTW, a well executed "full wave" voltage doubler is the economical way to obtain a high performance B+ PSU. Good sized caps. in the stack followed by a LC section reservoir get the job done, well. Hint: Hegeman, Marantz, and McIntosh used the method.
I have Blencowe's hifi book. I'm planning on using one the power supply examples.
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Old 15th November 2020, 05:43 PM   #19
Eli Duttman is offline Eli Duttman  United States
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In any power handling range, push/pull "iron" costs less than the SE stuff.

All sorts of signal topologies are available to chose from. "Baby Huey", "El Cheapo", and the Dyna ST-35 are some of them.

You will be very hard pressed to find a more economical high performance setup for the B+ PSU than "full wave" doubling a boosted Triad N-77U with UF5408 diodes.
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Old 15th November 2020, 10:04 PM   #20
6A3sUMMER is offline 6A3sUMMER  United States
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Eli,

That is a good way to get the B+.
But just be sure to keep all of the doubler circuit in a local loop. Extending it out to
other areas of the amplifier, it will cause terrible hum/hum upper harmonics noise.
But it requires one more tran$former, the filament tran$former.

Choke input full wave with center tap, or with bridge, has the quietest hum/hum upper harmonics ground loop noise. Again, be sure to keep the circuit to just a local loop (at least the secondary, rectifiers, choke, and the first cap (and resistor and second cap).
But the power transformer is more expen$ive, and heavy; and so is the added choke more expen$ive and heavy. And, the choke needs to be far away from the output transformers, and oriented properly.
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