Suppo Audio -- New Chinese EL84 PP amp for CHEAP.

[Bosk]

Originally Posted by thoriated

Hi, all -

Can anyone recommend a chinese manufacturer of top quality output PP transformers in the 25-35 watt range 8K:4/8/16 ohm like the Tamura F685 but not *too* expensive? I have a 25W/channel compact amp project in the works.

I know that VT4C.com sell rather cheap output transformers here:
Audio Catalog

I can't vouch for the quality of their transformers however, having not tried them myself.

[tubesteve]

so far, i have used different suppliers here. the results average to bad, for PP and SE.
most tube amp manufacturers do the transformers by thenselves in order to save costs.
Most transformers are done on an Ei core with Z11 material, claiming, imported from japan. many of the transformers failed a HV safety-test in our lab or other things maybe wrong such as winding directions, windings cancelling each other. for SE, the airgap ist just not existing , metals are screwed together without insulation of the screws.or they have a bad frequency response, which is the corrected by stron NFB. or, you order today in a company, if you want repeat order, the company does not exist anymore...

[OneyedK]

Originally Posted by bigjppop

I've heard its a bear to remove tube sockets from a PCB but I've never tried it. Any suggestions here?

First remove as much solder as possible.
Then cut the pins.
Remove the socket.
Solder the pins out, one by one.
Any other method will take too much heat and time.

Originally Posted by Bosk

I may do the triode mod too, though I may need some more detailed instructions as I'm not sure precisely what values of resistors go where.

Suppo uses 3 identical cathode resistors parallel in each channel, easy to recognise.
Remove them and replace them with 2 resistors of 390 Ohm (2 or 3 Watts) in each channel.
I placed them on the underside of the pcb to be able to change them if necessary.

I stayed on the safe side there, some tubes certainly can be biased hotter.
360//360 as cathode resistor will be better for some tubes, but then again,
if you want to do some "tube rolling", you better stay on the safe side.

Rest of the instructions:
Small error, I marked the cathode resistor as 185, that should be 195 ohm (390//390).





Somebody mentioned that connecting grid and anode the way I do, might cause oscillation,
but when I asked for a technical explanation, silence was the answer.
From my knowledge of 6P15 and EL84, when correctly biased, this is not possible.

[bigjppop]

Thanks for the detailed instructions on the triode mod. I think I can handle that.

Also, thanks for the input on removing the sockets. It sounds like to get them out I'll pretty much have to destroy them and replace them with new ones; is that about the gist?

[OneyedK]

Yes, that's correct.

If you want to be able to cut the grid trace as close as possible to the pin, you will have to replace one socket.
You can leave the socket in, if you want to cut a little further away from that pin.

[Gorgomat]

Hello,

it was me who mentioned the fact that a direct connection might cause parasitic oscillation if the connection is too long. Well, I have tested (and measured ) both connection types with and without the 100 Ohm resistors. Using a 100Ohm resistor is the safe way to go.

Best regards,

George

[PJJ]

Hi Guys
I am new to the forum (first post) so please forgive me if this is in any way incorrect.

I like the look of the Suppo GV-1 which has generated much comment here, indeed I have sent a few e-mails to them but a lack of any response makes me nervous of dealing with them. Are they still in business?

I wish to build my own Amp and I have read the threads on the Chinese Amps with great interest. Indeed I am of the opinion I may be better off buying one of these Amps and moving the components into a chassis more of my liking.
Is this a good way to start?

Opinion seems divided as to their quality of components and design, so would I be better off trying to find good circuit diagrams for me to attempt to build as my experience increases?
Thanks in advance
Peter

[Bosk]

OneyedK, thankyou very much for your help!

I'd like to go ahead and perform the Triode mod but being a newbie to tubes would like to be absolutely sure I know what I'm doing!
Could you please be so kind as to confirm that the following procedure is correct?


Suppo EL84 Triode Mod:

- Solder pins 7 & 9 of all four EL84 sockets together.
- Cut PCB traces from pin 9 on each EL84 socket.
- Replace resistors in the following manner:

[tubesteve]

for those who wish to make their own amp: start from the scratch is my best advise. doing so, there is something to learn and understand. some circuits on the internet have also some flaws and often the mains transformer delivers a different voltage under load, so that a claimed DC operation point of the valves in nearly not guaranteed. making its own design includes more fun, as well. let the chinese do the copy jobs.

[tubesteve]

i found some pictures from inside suppo. the pictures maybspeak for themselves, here the link:
Google-Ergebnis für http://tyhong.com/audio/pic/workshop_s.jpg