Greenvalve 10y into 801a

[bravi]

Thanks Ray for your response. My rationale for looking at this option, is same as yours, quad by pass and age. Anything over 20kgs handled with caution.
My out put transformer for the planned 813 amp are around 5kgs each!
As advised, I will check other forums as well

 

[triode_al]

Hi, I am working on a 10Y (7.5V/1.1A) output amplifier. I think of using a 4V/1A DHT for input.

And I was first looking at 4Kg transformers for 10Y. . . Same background here to make it light - a heart issue too. I once had: mono units 15 Kg . Now: Max < 8Kg for a stereo case.

So - I found some new developments at A lie express:

• 220V DC output SMPS = Half-bridge LLC Quasi-resonant 600W Power Amplifier Switching Power Supply DC24V36V48V60 Single Voltage Can Be Fine-tuned. That does have power. Price € 50,- Two makes 440V! And gives a filament supply at half the Vb so this can be used for a cathode follower. .. Soft start control.
• High power switch power supply KT88 300B electronic tube power amplifier stabilized voltage = Output voltageC 200V-520V can be customized. At € 120 incl ship not cheap at all but looks good on paper (like a lot on that A Lie site)

The various supporting supplies are independent to ground (connected with a 1MΩ resistor for beelding), floating: each group are independent output. One of them is an ideal bias supply.
So that makes a very attractive unit.

Also I found Meanwell has a series of medical SMPS supplies - the EPS series. They have a low leakage and I think could be used for a DHT. So that makes and other building block. I like the 7.5V/8V version. It has some headroom for a CCS/FET.

 

[sumotan]

I've built a few 10Y stages, including 2 or 3 with the 126C. In one of them I used 2 126C in series just as plate chokes. Ridiculous use of real estate but it did actually sound a little better.

My view would be:

• Use filament bias on the 10Y to avoid a cathode bypass and also to avoid SIC diodes, which I ripped out of all my equipment and replaced with resistors. Better sound, smoother and more musical. The SIC diodes had a kind of glare I couldn't live with.
• Use just the primary of the 126C as a plate choke and use a Russian FT-2 or FT-3 coupling cap. You'll get a cleaner and better sound. Incidentally, you can't add the primary and secondary to make a larger value plate choke. Doesn't work in practice, and believe me I tried all ways.
• Use one supply with Rod Coleman regs for each tube. So total 4 supplies.

For any cathode bypass caps, use DC Link caps. Vishay or Kemet I've used and sound great. I haven't tried Epcos or Wima DC Link caps but they probably sound equally good. I never used an 801A in the output so no comment there. Anyway, you should get good sound, though not too much output. I know nothing of A2 operation, but I know that works and I've heard it in a high sensitivity horn system sounding very nice. Maybe others could say a word about that and include a schematic.

.

Hi Andy,
Slightly OT question. There's always talk about separating the PS from amp for best results. What if I build an amp in 2 tier, PS at the bottom & Analog circuit sitting above, would this reduce emf etc ?

Thanks

 

[andyjevans]

The thing about having a separate PSU for B+ is that if the umbilical is too long you could get HF rolloff. I did with a 1 metre cable. It didn't seem to matter too much when I had an outboard filament supply. So these days I use one chassis or at least locate the B+ right next to the main circuit.

 

[Rod Coleman]

Hi Andy,
Slightly OT question. There's always talk about separating the PS from amp for best results. What if I build an amp in 2 tier, PS at the bottom & Analog circuit sitting above, would this reduce emf etc ?

Thanks

This is how I usually do it.

The amount of difference it makes is very variable -
For example:

• how short is the signal wiring?
• Are the transformers designed for low flux emissions?
• Any ITs or anode load chokes under the top plate?

Place all the power transformers close to their rectifiers & capacitors, with carefully routed short wires.
2-300mm distance from signal wiring will reduce risks of coupling from good quality transformers, 500mm or more might be needed for cheaper PTs.
Before drilling the chassis, Try measuring noise using a battery-power computer running ARTA. A USB soundcard with MIC input can reach very low-level noise. Moving the PTs to get best results is instructive.

 

[Francois G]

Hi all,

This summer I'll be plunging into the greenvalve design with 10y driving 801a, through hammond interstages and SMPS power supply.

I'll follow the schematic but will use 4 rod coleman regulators for the filaments.

This is my first DHT build, and how bias works is still beyond me.

What would you recommend? Filament bias on 10y, maybe with SIC diodes, and how many volts? And what to do with the output stage?

Any pointers on filament topology and values for this circuit are most welcome!

Cheers,
Simon

Would OP please be kind and provide a link to Greenvalve whatever! I searched and found plenty of gardening and hydroponics valves, but not the original circuit and context of the amp he wants to build.

 

[ratbagp]

https://greenvalve.wordpress.com/the-maxim-gm70/

The site is now private.

ray

 

[sumotan]

This is how I usually do it.

The amount of difference it makes is very variable -
For example:

• how short is the signal wiring?
• Are the transformers designed for low flux emissions?
• Any ITs or anode load chokes under the top plate?

Place all the power transformers close to their rectifiers & capacitors, with carefully routed short wires.
2-300mm distance from signal wiring will reduce risks of coupling from good quality transformers, 500mm or more might be needed for cheaper PTs.
Before drilling the chassis, Try measuring noise using a battery-power computer running ARTA. A USB soundcard with MIC input can reach very low-level noise. Moving the PTs to get best results is instructive.

Many thanks again Rod