Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Diverted on August 19, 2023, 12:17:29 pm
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I stumbled across a schematic for an Angela Super Single. Sounds cool, I have the right transformers so I thought I would try building it with reverb added in. I have previously built two or three 5W Champ circuits with reverb, and I'm happy with them.
Anyway, what do you think of this mishmash of a schematic? It's the Angela circuit blended with the schematic I previously used for the Champ reverbs (courtesy telentubes at https://ampgarage.com/forum/viewtopic.php?f=6&t=30988).
Have I missed anything on this schematic? The only thing I'm changing is ditching the 5Y3 and using diodes instead, but that's not super pertinent to the question of whether I fit it all together OK. Thanks! Apologies in advance for crummy photoshop.
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Had to look twice because my eyes are triggered to "push pull!" and it isn't.
It may be too sensitive to assemble as a combo: 1.2mV in for full output (we tend to 5mV-50mV). Take some gain out at V1B: ditch the cathode cap and then try about 4:1 attenuation at its grid. Or expand to the late AA-Champ 2(3)-knob tone stack.
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Thanks. I wondered about that ... the old version of the circuit I was building was fine (straight champ circuit w/reverb) but the Angela is a different animal.
I'm going to build this with terminal strips etc so I won't be locked in and can change stuff around. May also try a 12AY7 in V1 if it's too much. Thanks!
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I just finished up the amp and it's pretty impressive. Very quiet with a 125ma 5h choke, sounds great. Gets very loud.
Now that it's "done" I'm re-thinking the power transformer. Want to ask you all's opinions on it. If I do need to switch it out at some point it's not a big deal on the chassis I built.
Anyway, I am using a Hammond 270EX power transformer. The secondary is rated for 275-0-275@144ma. I'm using diodes for rectification duties.
I have heard some people online write that the transformer for this circuit should be rated for between 150 and 200ma on the secondary. Is 144ma enough? I've had it on for an hour or so at a time, a few times since building, and the transformer stays relatively cool.
Specs:
With a 390 ohm cathode resistor on the 6V6s, plates are at about 365-370vdc, tubes are biased at around 33ma each. Cathode voltage is around 25vdc, so the amp is biased around 86-90 percent.
Thanks!
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I guess you know you can go up to 100 % dissipation...
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Yep. But at the moment I don't have a cathode resistor on hand that will get me up to that limit.
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Getting back to the question, I just don't see how 144ma isn't enough on the secondary. Can anyone tell me something I'm missing?
Putting aside current requirements of the three 12A-type tubes, I see the 6V6s like this:
14Wx2/plate voltage=total plate current. So 28/370 or so = 75.6ma. Are there considerations I'm leaving out? Because if this is correct the transformer's just fine.
Thanks.
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Your output tubes are only pulling 64mA. I'd say your 144mA PT is just fine.
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Thanks Sluckey. That's what I thought but then I second-guessed myself and thought I had to be leaving something off. The 200ma suggestion some make for the Angela just seems like overkill.
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How do you like the reverb? Is it working as anticipated?
I am assembling a 2-tube reverb Champ at the moment. It is close kin to your circuit with the same preamp/reverb tube compliment, but just the one 6V6 & a TMB Twin tonestack.
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The 200ma suggestion some make for the Angela just seems like overkill.
200mA for 2 x 6L6GC most likely
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....The 200ma suggestion some make for the Angela just seems like overkill.
Two 6V6 is a DeLuxe. Nobody puts a 200mA PT in a stock-like DeLuxe.
Yes, SE class A "can" be more heat than a cool-bias P-P at idle. But the usual P-P g-amp builds are not super cool (not like battery beach radios) and anyway we PLAY our amps not let them sit idle.
And I can't think of many venues/gigs where if a one-6V6 amp was "fail!", two 6V6 would be clam-happy.
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Yes, most of mine get pretty hot! Thanks, I don't play around with SE too often.
Actually just checked in for some advice.
What would be the most effective way to switch between single tube output stage and both? I'd like a scaled down option too.
The cathodes share an RC network so I would need to separate those.
What, then? Use a double pull switch to cut heaters to one 6V6, simultaneously going from 8 to 4 ohm from the output transformer?
I'm sure there are less cumbersome ways to do this.
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played around with 2SE builds. Experimented with pulling 1, changing the speaker, playing. never found a case where pulling one tube made the amp sound better. It's "sound" comes from the pair, similar to a V1 tube that's strapped parallel sounds different than a just a V1A.
played with 6K6, 6V6, 6L6, settled on 1 KT88
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How do you like the reverb? Is it working as anticipated?
It works great. No hum, it's very clean. And there's actually so much reverb that I swapped out V2 for a 12AU7 in place of the 12AT7.
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Hi all, I think I will drop the idea of a half power switch.
However, wanted to get some unrelated opinions. In an earlier comment, PRR wrote that the amp might be too sensitive as built.
It certainly is a beast, and with a 12AX7 in V1 and V3, and a 12AT7 in V2, it had some issues when I had the cathode bypass switched in and the 25uf cathode cap on V1A switched in. When driven hard above about 6 on the volume pot, I was getting choppy, static-y remnants on notes as they faded, particularly in the lower register. Is this due to the output tubes being driven just too hard and not being able to handle it? With the 6V6s running with no cathode bypass capacitor, and with V1A switched to the smaller cap, it was not an issue.
And with everything maxed out, and a 12AY7 in V1 and V3, it's also not an issue, though every once in a while I get a squeal when playing loud.
Any suggestions on how to address this? Went through updated voltages today, here's what I have
B+: 389
B+1: 379
B+2: 363
B+3: 313
(1K resistor between B+1 and 2, 8.2K between B+2 and 3.
V1A pre
P 150
C 2.8
V1B pre
P 152
C 2.6
V2 REVERB DRIVER
P 352
C 19
V3A REVERB RETURN
P 152
C 2.4
V3B last gain stage
P 152
C 2.4
V4-5
P 371
C 23.3
G1: 360
C1 32.8ma
C2 33.1ma
Cathode resistor: 335.5
Tubes running at approximately 82 percent.
Thanks!
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scope will tell you where you're overdriving.
my thumb rule in SE;
PA cathode VDC is ~~~~~ the MAX clean signal you can give the PA tubes before they clip/compress
so you have 23vdc a Ck, you can hit G1 with ~~~~~~23 VAC
now if you're only hitting it with 17VAC but it looks like a train wreak then the PA will amplify that wreak
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Unfortunately I do not have a scope so I can’t take a look.
I may just try reducing overall gain by removing a bypass cap, perhaps V3B as suggested earlier. Any ideas?
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It may be too sensitive to assemble as a combo: 1.2mV in for full output (we tend to 5mV-50mV). Take some gain out at V1B: ditch the cathode cap and then try about 4:1 attenuation at its grid. Or expand to the late AA-Champ 2(3)-knob tone stack.
Thanks. I did take out the v1B bypass; helped a bit. But can you elaborate on attenuating the grid? I am not getting the choppy remnants/clipping when I have it maxed out so much now. However I worry about parasitic oscillation as moving my hands near/cupping them around the 6V6s will cause the amp to squeal. Not sure what that is all about.