My impression was that it was driven by practicalities rather than for performance. I have not been able to compare since I had the wrong transformer for the EL84 version (with the power supply on the same board); I interpreted the '275VAC' on the PCB a bit too literally. The project was put to one side pending a suitable transformer turning up, and I am yet to get around to it again.
Hi I need some advice. and I am hoping you guys can help. I am Planning to build a stereo version of this amp.
I have the following transformers and not sure if they would be suitable for this project.
I have a power transformer with secondaries :
1. 0-340Vac : 0.7A
2. 0-6.3Vac : 6.8A
3. 0-50Vac : 0.1A
2 x output transformers
Primary windings PWPP30W6K6 https://primarywindings.com/product/30w-6600-ohms-ultra-linear-push-pull-output-transformer/
These have a primary of 6.6K, are rated at 30W, and have 40% UL taps. can these be used in this amp?
any advice would be greatly appreciated!
I have the following transformers and not sure if they would be suitable for this project.
I have a power transformer with secondaries :
1. 0-340Vac : 0.7A
2. 0-6.3Vac : 6.8A
3. 0-50Vac : 0.1A
2 x output transformers
Primary windings PWPP30W6K6 https://primarywindings.com/product/30w-6600-ohms-ultra-linear-push-pull-output-transformer/
These have a primary of 6.6K, are rated at 30W, and have 40% UL taps. can these be used in this amp?
any advice would be greatly appreciated!
Your transformers are fine and can be made to work well in a BH amplifier, with some adaptation. Your PT certainly has enough HV current capacity. As you may have seen, the intended power transformer is the this one: https://sklep.toroidy.pl/en_US/p/TSTA-0250001-Mains-transformer-for-tubes/648. The main difference is it’s higher 6.3 V current capacity.
You did not mention which output tubes types you have in mind. With your heater supply of 6.8 amps you are at the maximum with what EL34 demands (4x1.5 +2x0.3 = 6.6 amps). Using 6L6GC/6P3S-ev type output tubes will allow more of a safety margin on the heater supply and will work well with your output transformer’s input impedance. The 340Vac is a bit too high, but you could control that in several ways to achieve the desired 425-450Vdc supply.
Check out this discussion here. Your situation has some similarities. https://www.diyaudio.com/community/threads/el34-baby-huey-amplifier.326920/page-78#post-7492457
Good luck.
You did not mention which output tubes types you have in mind. With your heater supply of 6.8 amps you are at the maximum with what EL34 demands (4x1.5 +2x0.3 = 6.6 amps). Using 6L6GC/6P3S-ev type output tubes will allow more of a safety margin on the heater supply and will work well with your output transformer’s input impedance. The 340Vac is a bit too high, but you could control that in several ways to achieve the desired 425-450Vdc supply.
Check out this discussion here. Your situation has some similarities. https://www.diyaudio.com/community/threads/el34-baby-huey-amplifier.326920/page-78#post-7492457
Good luck.
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7581A might work, 6L6GC characteristics, higher ratings. An 807 would do for sure, plate caps though. I've had really good luck with 6L6EH (Electroharmonix). They will survive in a Fender Twin without any trouble. Those look much like a 7581A inside.
For EL34 amps, I use 6CA7, which are beam power tubes. They also don't cook their bases to pieces as the average EL34 is happy to do.
I agree 100% with Francois. You really want some safety on heater current as some tubes may draw more than others (for example). You also would like the power transformer to run a little cooler if possible.
For EL34 amps, I use 6CA7, which are beam power tubes. They also don't cook their bases to pieces as the average EL34 is happy to do.
I agree 100% with Francois. You really want some safety on heater current as some tubes may draw more than others (for example). You also would like the power transformer to run a little cooler if possible.
This is fine with the 6k6 load. Land around 450V B+ and you'll be fine. I use something similar.
Quite tight for EL34: you'll need 6.6A and I don't know how overdimensioned is.
This is a bit tight for the negative side of the voltage for the powerdrive.
You'll be able to go above 40 Wrms per channel, the OPT could become the bottleneck.
Your Power transformer (PT) is well overrated in current capability on the HV (340Vac) coil, and will run cool, so I think we could be less concerned about running the heater coil close to it’s limit.
Since you have the EL34s already I’d say go for it, as long as you carefully monitor the power transformer temperature. If the PT gets too hot you could add a helper 6.3 Volt heater transformer such as this one. The transformer in my link is higher current than needed, but serves as an example.
https://www.mouser.com/datasheet/2/410/VPS12_6300-781411.pdf