My low watts projects

[katabatic]

Two more small amps, that I completed last month.





/ed B in NC

I've now completed my version of the 6bm8 amp (Ed's one on the right). I used a Hammond 369x power transformer, Edcor GSXE 10-8-5k output transformers, and Soviet-era 6f3p tubes. Coupling caps are Russian K40-Y-9's. It sounds great, a little 'darker' than the Get*Set*Go and Darling that I've built previously (darker meaning, I think, more pronounced bass). I used both NFB bits, the one in the original schematic and Ed's 1 meg resistor version. Many thanks to Ed and Ty for putting the plans up here.

George

[EWBrown]

Very nice! Much neater layout and wiring than my 6F3P / 6Ф3П / 6BM8 amp, which was wired in "layers" because of the limited under-chassis space.

If I were to do this again (and I probably will) I won't try to make it so small and crowded.

I would imagine the Edcor GXSE10-8-5K OPTs would sound even better than the smaller TF103s.

As previously mentioned, I found that the dual-NFB approach seemed to work the best. I've tried this with other tubes, with lesser results. Must be something unique to the 6BM8 family

Almost time for me to head to the neighborhood Memorial Day Weenie Roast

/ed B

[azazello]

My new SE 6S4S /1957-s/ & EC86-Phillips with interstage trani P-T 156 http://diyparadise.com/web/learn-learn- ... ransformer and output transf. EDCOR CSE 15-8-5. But CSE is small with small iron and band starts with constant amplitude from 50-60 Hz. I will change to EDCOR 25W or Hammond 25W. Sound is very clear and clean! /EDCOR sounds very good/.
Amplifier is without caps in signal paths, bias 6S4S is fixed.
https://picasaweb.google.com/1095707775 ... 1317018466
https://picasaweb.google.com/1095707775 ... 4015244242
https://picasaweb.google.com/1095707775 ... 5252280914

[azazello]

The best output transformer is.....missing transformer!
My last try - OTL PP PSE - 6AS7GA GE & ECC81-RFT & PCC88-Tesla.
4 PSU channels for every channel. Very clear sound with very deep bass.
https://picasaweb.google.com/1095707775 ... 0833103202

[soundbrigade]

... missing transformer.

No I'm not there really. Still struggling with various projects but always being sucked back to my PC.

[Geek]

... missing transformer.

No I'm not there really. Still struggling with various projects but always being sucked back to my PC.

YES!

I could be doing so many wonderful things if this box would stop making me look at it!

[kku]

A 12B4A SET schematic using tube rectification. Another dirt cheap SE!

http://www.enjoythemusic.com/magazine/e ... vinson.htm

Now I'm aching to make a small point to point wired amp.

[soundbrigade]

I have tried that one out but with poor result. Couldn't get rid of the hum.

[kku]

That is unfortunate. I wondered about that issue since the schematic shows only one grounding point and I couldn't figure out which additional parts should I connect to ground bus. I guess I'll try the Darling schematic with 12AX7/12B4A's.

[soundbrigade]

I guess, but this is a wild guess that as I had to drop the voltage from 355 till 200V, something happened on the way.

[kku]

I guess I'm staying away from that design.

Can anyone recommend a good EL84 SET design? 6BM8 spud amp is great but NOS 6BM8 are scarce compared to EL84. With EL84 design, one can always tweak heater supply to use cheap 8BQ5/10BQ5 tubes.

[soundbrigade]

Don't drop it because I wrote something negatively, I've got 3-5 other disgns that are less "complicated". I can fix schematics for you tomorrow.

There's a design called RH-84 which is pretty popular. Tom Mcnally has built it:
http://www.diytube.com/phpBB2/viewtopic.php?t=5223&sid=9c3944b38b19961647e13037e89ce9b5

[Shannon Parks]

EL84 SET? I'll up the Budgie SE schematic very soon. Boards coming next week. Technically a SEUL, but one can mod it as much as they wanted (triode, RH84,etc.).

Shannon

[EWBrown]

If 6BM8 / ECL82 / 6Ф3П are hard to find, or too costly, there are low cost replacements: 8B8, 8V filament; 11BM8 11V filament, 12V is OK; 16A8, 16V filament, and 50BM8, 50V filament. These can be operated in Pentode or UL mode with good resullts, and triode mode for lower output power.

Same pinouts, same basic triode and pentode operating characteristics, just different filament requirements.

I've used 11BM8s and 16A8s in numerous designs and builds, including two modified K-502s, which can use either tube type, with a filament voltage selector switch hidden under the chassis.

Then there is the Russian 6Ф3П, which is a direct ECL82 / 6BM8 plug in replacement. I've also used these, they are generally quite good.
The Chinese 6F3 is of variable quality, some are good and some just plain stink...

6GV8, 9GV8, 10GV8 and 11MS8 are similar, but their pinouts are not 6BM8 compatible. These tubes are not good for Ultralinear operation - I've tried them, and they definitely do not like operating in this mode. Perhaps they need other than a 40% UL tap, perhaps 50% ?

/ed B

[EWBrown]

Some more EL84 equivalents, just a slightly different pinout; 6GK6, 10GK6, 16GK6 and 29GK6. These all have the same gm and rp of EL84 and 6BQ6, just with a different pinout and filament requirements. 8BQ5 and 10BQ5 are same as 6BQ5 / EL84 but with 8V or 10V filaments, these are much lower cost than the 6V versions.


Warning - PL84 is not a 15V version of EL84, it is a 15V filament version of EL86, or an equivalent of a 15CW5, and will blow up or melt down if run with typical EL84 plate voltages. The pinouts of the XCW5 family are same as 6BQ5, but there, the similarity ends, they are good tubes, but require lower B+ (200-250V) and a higher plate current, and lower Z OPTs.

/ed B