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    Building, troubleshooting and testing of these amplifiers should only be
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    the safety precautions around high voltages.

Dynaco ST-35 Circuits

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Thanks Ian, I must have missed those ones flipping through Ebay, I'll keep them in mind.

I was hoping you might elaborate a little more on the 6SL7/6v6 Huey you are running, as there is a comment on the wiki (Baby Huey PP EL84 amplifier - diyAudio) that makes it sound like it is not a worthwhile combination. Were there any changes to the circuit you made outside of adjusting for the different tubes?
The 6V6 / 6SL7 BH is the same as the schematic shown at post #602 in the BH thread with one change, the 47K / 220 K anode to anode connections with 16K cross connect resistor is 39K / 180K with 13K cross connect. There is also a resistor change in the current source on the 6SL7 diffamp tail to get the 6SL7 currents up marginally (around 0,7mA per triode rather than around 0.6mA for the 12AX7). The current Source loads on the mosfet sources followers have also had a resistor change to get the operating current up to 3.2 mA.

Theoretically the 12AX7/EL84 version should be better but there is just something about the 6SL7/6V6G version which is drop dead gorgeous. One of those instances where the theory is "the way to go wrong with confidence". It is built with Hammond 1608 Output Trannies, Your ST-35 Trannies are almost certainly superior to the Hammonds.

I will be following your progress with the El-Cheapo, as a simple design (no current sources, source folowers etc.) it is about the best that can be done, a good design. My EL84 BH prototype started life as a Morgan Jones "Bevois Valley" which is similar to an El-Cheapo.

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1608's are basically the same price as the z565 reproductions, so it's a pretty simple decision.

I have to agree with you on the look of the octal tubes...now I'm doubting my decision again... good thing I won't be ordering parts for a little while.

What are you using for a PT? If I'm reading the schematic right it looks like it its go 285v secondaries rated at 100ma, though a quick look through the usual suspect's websites doesn't show anything matching that with 6.3v and 5v secondaries as well.
...Theoretically the 12AX7/EL84 version should be better but there is just something about the 6SL7/6V6G version which is drop dead gorgeous. One of those instances where the theory is "the way to go wrong with confidence"...

Hi Ian,

I wonder if it's the 6SL7 or it's the 6V6G's that give you that drop dead gorgeousness.

I have a chassis already drilled for 9-pin sockets, so I'm thinking I could use either EL84, 6P1P, or even 6P43P-E. I also have a large selection of 12AX7's to choose from, including some Telefunken oldies. Have you ever used a combination of 12AX7 and 6V6? If so, does that fall short of the 6SL7 and 6V6 combo?

A combo of 12AX7 and 6P1P could make for a super-cheap BH variant, at least as far as the cost of tubes is concerned.

I'm starting to wonder if I should maybe upgrade my speakers before building a new amp. Maybe someone here could provide some suggestions that would go well with the amps discussed here. I would have about $250 to spend on drivers and crossovers. I'm a competent wood worker so complicated cabs aren't a problem. I'd be looking at bookshelf style speakers, probably 2-ways or maybe full ranges.

Modern rock is my bread and butter (lately fairly agressive , I also listen to jazz, a fair bit of folk, classic rock, blues, and mishmash of other things. I have fairly eclectic tastes that drift within certain ranges over time. I like clear, tight, prominent bass, and speakers that are not tiring to listen to. If it would be helpful I could put together a 5 or 6 song playlist that would run the gamut of music I listen to most often.

I looked inside the amp on the weekend to see what I'd done.

The power tranny is 260V 220mA (no centre tap) with 2 off 6.3V windings. I used one heater winding for each channel, common B+ supply.

I added a second power tranny a 4.5VA 15-0-15 Volts at 150mA (it cound have been even smaller). I used a doubler circuit (4 diodes, 4 caps) to generate a +80V, +40V, -40V, -80V supply. The mosfet souce followers ran between the +40 and -80V rails, the front end diffamp curtrent source tail returned to the -40V supply. The +80V supply was'nt used in the end and so I could have deleted it by removing one diode and 1 cap.

It is the 6V6G tubes which are drop dead gorgeous but I'm sure that EL84 can be made to sound as good using the same drive method. My EL84 amps (mono blocks) are sitting on the shelf waiting modification
I have power and output trannies to build:
1) A quad of EL84 per channel version for about 20 Watts per channel
2) A KT88 version for about 60 Watts per channel.
So may spend my time on one of those instead.

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Thanks Ian, I've done some more reading in the original, very long, thread for the huey and was thinking a Hammond 270HX (550v 230mA, 6.3v 6A, 5v 3A).

Unfortunately, shortly after posting the above musing about new speakers, the tweeter in one of my speakers has gone out (not available, or worth replacing if it were), and i've been forced to switch to an old hometheater in a box for listening. It is an unfortunate, murky, muddled, hissy, and boomy sounding beast, that produces a horrible ringing (about 6kz according to my PC's eq) under certain circumstances. As I now have no speakers for a tube amp to drive, and the home theater makes me want to stab chopsticks into my ears, I will be delaying the tube amp to build new speakers.

Now I'm trying to find a full range or 2-way that will be both befitting of a high quality tube amp, but leave me enough money to build said tube amp by summers end. Unfortunately I just keep finding big and expensive speakers I'd rather build. I'm also toying with they idea of picking up some vintage loud speakers, redoing the cross over, and holding off on new speakers until after I have a valve amp up and running.

Decisions, decisions.

I look forward to your updated BH schematic. I was curious if you had any thoughts on what, if any, changes to the BH circuit might benefit the z565's? They have a higher power rating (17.5w) than the 1608s, (I think a 6v6 is good for 14w?), or if they might benefit from global NFB, which I see you haven't used in the fixed bias huey?

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