I figure I might as well stop hijacking the "Cheap SE Transformers" topic 
Did some more tweaking over the last couple of days.
Main circuit - only changed NFB resistor and dB value.
New F3: 19Hz to 23KHz @ 1W into 8 ohms.
Max clean power into 8 ohms, 2.85W. 3W @ roughly 8-10% (gotta build me a distortion meter). Of course, less NFB distortion correction = less output power.
Square response, ruler straight with only slight corner rounding on the bottom of the trailing edge, due to xformer above 5KHz. Ringing, zero. Spikes, zero. Nasty top-leading edge spike at extreme overload. Spike, not ring.
PS circuit in the next post...
Did some more tweaking over the last couple of days.
Main circuit - only changed NFB resistor and dB value.
New F3: 19Hz to 23KHz @ 1W into 8 ohms.
Max clean power into 8 ohms, 2.85W. 3W @ roughly 8-10% (gotta build me a distortion meter). Of course, less NFB distortion correction = less output power.
Square response, ruler straight with only slight corner rounding on the bottom of the trailing edge, due to xformer above 5KHz. Ringing, zero. Spikes, zero. Nasty top-leading edge spike at extreme overload. Spike, not ring.
PS circuit in the next post...
Attachments
Power supply went through a bit of a makeover. C-L-C-R-C seems optimum.
Feeding the first stage straight to the second C. SS CCS makes the isolation resistor moot.
Because of the added C, the voltage went up and I had to up the "B" resistor value and watt rating.
Floated the filaments at around +60V for hum elimination (as opposed to reduction).
Choke could still be 5-10H though. 120Hz hum is about -80dB down. I'd like it better than -100dB.
Ordered the final parts from Mouser today. Hope to have pics in a week or so.
Feeding the first stage straight to the second C. SS CCS makes the isolation resistor moot.
Because of the added C, the voltage went up and I had to up the "B" resistor value and watt rating.
Floated the filaments at around +60V for hum elimination (as opposed to reduction).
Choke could still be 5-10H though. 120Hz hum is about -80dB down. I'd like it better than -100dB.
Ordered the final parts from Mouser today. Hope to have pics in a week or so.
Attachments
Nice design! Have you thought about trying cathode feedback for the output stage through the OPT secondary instead of global feedback? I tried this on a 6EM7 amp using Hammond 125ESE's and was stunned by the improvement. I don't know how it would compare with other feedback circuits, but it might be worth a try.
Kyle
Kyle
Re: Hi Jack!
Thanks!
No I haven't tried some CFB, but shall do so ASAP
Yes.
they are apples and oranges. Even trioded, you still need ~8K on the 6BM8 for 600mW out. Great for a headphone-only amp. I have some 8K SE OPT's around here somewheres...
If you wanna hear a "1 watt 300B" that's a true-triode, use a 6AH4GT at 250V and 5K plate
Kyle K said:
Thanks!
No I haven't tried some CFB, but shall do so ASAP
moray james said:
Yes.
they are apples and oranges. Even trioded, you still need ~8K on the 6BM8 for 600mW out. Great for a headphone-only amp. I have some 8K SE OPT's around here somewheres...
If you wanna hear a "1 watt 300B" that's a true-triode, use a 6AH4GT at 250V and 5K plate
All put together for tomorrow's Northwest Audiofest
Schematic with final specs.
Excuse my crummy digi-cam
The switch on the left is "speakers on/off" with the phones jack right below it.
Cool thing is the finish matches my speakers!
That's the power switch on the back. I had put it there to keep the AC wiring as short and to the point as possible to reduce hum. However when I did a bench test, I purposely swung AC line down the side it "would have been" for a front mounted switch and hum was not an issue. So the production unit will have the AC switch front mounted, opposite side of the chassis from the speaker switch.
Also the transformer is covered (I used a surplus Z-mount that was old and ugly) here. The future one will have an exposed Edcor XPWR-106.
Schematic with final specs.
Excuse my crummy digi-cam
The switch on the left is "speakers on/off" with the phones jack right below it.
An externally hosted image should be here but it was not working when we last tested it.
Cool thing is the finish matches my speakers!
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
That's the power switch on the back. I had put it there to keep the AC wiring as short and to the point as possible to reduce hum. However when I did a bench test, I purposely swung AC line down the side it "would have been" for a front mounted switch and hum was not an issue. So the production unit will have the AC switch front mounted, opposite side of the chassis from the speaker switch.
Also the transformer is covered (I used a surplus Z-mount that was old and ugly) here. The future one will have an exposed Edcor XPWR-106.
An externally hosted image should be here but it was not working when we last tested it.
I had the pleasure of meeting Gregg yesterday, We got to swap stories 7 interesting tidbuts.
It is a lovely little amp... we discussed a few improvents, but all-in-all a lovely addition to available projects (& Gregg says he is going to get kits together)
Here is my pic with no fancy drapery.
dave
PS: Gregg, did you see where my little red screwdriver went... i think i must have left it on Al's ping pong table.
It is a lovely little amp... we discussed a few improvents, but all-in-all a lovely addition to available projects (& Gregg says he is going to get kits together
)Here is my pic with no fancy drapery.
dave
PS: Gregg, did you see where my little red screwdriver went... i think i must have left it on Al's ping pong table.
Attachments
Hi Dave,
Look foward to swapping a ton more stories in the future!
Hopefully I'll have the info soon
That was embarrassing overlook on the terminals, LOL! I put the thing together and realized, oh... I guess I should have seperated the terminals by the standard 3/4". Nah, who will notice? Dave, the look on your face was priceless when you made the discovery!
Yeah, that's where I last saw it.
I almost grabbed it, then realizing it was yours, I put it on the table near the baffles. As one of the last ones to leave, that's where I still saw it as I grabbed my CD changer.
6AH4GT is harder to get than a NOS 300B. Grab what you can, where you can and don't be surprised to start paying upwards $30/ea. for them
I'd recommend this tube for anything requiring 1 watt.
I actually wanted to go with it first, but availability made me scuttle that plan. I do plan on a limited-release 6AH4GT version of this amp if I can score enough.
Soundwise, it's an absolute 1-watt wonder!
Look foward to swapping a ton more stories in the future!
planet10 said:It is a lovely little amp... we discussed a few improvents, but all-in-all a lovely addition to available projects (& Gregg says he is going to get kits together
Hopefully I'll have the info soon
That was embarrassing overlook on the terminals, LOL! I put the thing together and realized, oh... I guess I should have seperated the terminals by the standard 3/4". Nah, who will notice? Dave, the look on your face was priceless when you made the discovery!
An externally hosted image should be here but it was not working when we last tested it.
planet10 said:
Yeah, that's where I last saw it.
I almost grabbed it, then realizing it was yours, I put it on the table near the baffles. As one of the last ones to leave, that's where I still saw it as I grabbed my CD changer.
Looneytunes said:
6AH4GT is harder to get than a NOS 300B. Grab what you can, where you can and don't be surprised to start paying upwards $30/ea. for them
I'd recommend this tube for anything requiring 1 watt.
I actually wanted to go with it first, but availability made me scuttle that plan. I do plan on a limited-release 6AH4GT version of this amp if I can score enough.
Soundwise, it's an absolute 1-watt wonder!
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