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A Very Compact Hybrid Amp - Page 67

post #991 of 2203
4/28/09 at 3:02am
mr slim, I am using an 8416, which worked fine a soha II, and i have two and both behave identically. I can try a 6n1p but its consuming so little current on that triode, i guess something is wrong.
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post #992 of 2203
4/28/09 at 3:04am
12au7/A variants
ecc82
6680
6189
5963
7316
5814
6922
6dj8
8614 (12.6V 6922)
6n1p
6N23
12bh7/12bh7A
6BQ7

The heater supply will accommodate 12.6V and 6.3V tubes running anywhere from 150mA to 600mA.

The front end servo will accommodate many types of tubes. Its design center is around the 12au7 type.

Amp Features
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post #993 of 2203
4/28/09 at 3:06am
My CTH has arrived from sachu, just gotta wire up the various connectors and switches, house it and we're good to go
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post #994 of 2203
4/28/09 at 3:07am
Thanks guys.

I'll be using the small Hammond case with the pref top from Spruce Canyon Labs. I wanted to put a 1/4" on the front and mini jack on the back but it looks like with the fuse, power switch and heater switch on the back there won't be room... still I might give it a shot.

I'll be using Sonicap Gen II for the coupling caps.

Wiatrob, I don't have a problem with your heater switch except that I hate cutting square holes. But I think I can get away with a round hole and still have it look good. You're right about the arming-type toggles - they would be too large.

I'll wait till I have the Sonicaps and the case work done before I power this up.
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post #995 of 2203
4/28/09 at 3:15am
I tried the 6n1p, and same result. This is looking like the CRD is the problem.

anyone got a spare? I cant source them in the uk.
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post #996 of 2203
4/28/09 at 3:24am
I have a quick question for all you CTH geniuses.

I have a spare switched pot from an AMB mini3 and was wondering if I could use that as the main power switch as well as pot. It seems a more elegant solution to using a separate switch for power.
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post #997 of 2203
4/28/09 at 3:38am
Other then being a major PITA to wire it should be OK (the switch in those pots is rated for 16 volts DC @ 3 amps).
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post #998 of 2203
4/28/09 at 4:02am
why pain in the ass? I take it it's the two connectors at the back.
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post #999 of 2203
4/28/09 at 4:05am
Quote:
Originally Posted by smeggy View Post
why pain in the ass? I take it it's the two connectors at the back.
Sounds like a good idea, maybe built in to REV.2 so no wiring is necessary?
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post #1000 of 2203
4/28/09 at 5:39am
You have to run one of the AC lines to the front. It won't be horrible. The only thing I don't like about those pots are the tapers. However, you can drill out the studs, separate the pot, and put in a 15A taper pot onto the front, with the switch in the back.

Or you can use a pot extender, depending on how you are wiring it and if you're going with a larger case. I never could properly align those extenders though.
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post #1001 of 2203
4/28/09 at 8:13am
@rds - Your pics look great - perhaps Bill could use them on the site somewhere for builders to compare to prior to pwrup... Your C5P & C10P look tall sure it will slide into small case? Edit: I could be wrong, my builds are older when we had shorter/fatter C5P & C10P].
And my what patience you have waiting for C4s

@adamus - I've no CRD spares, even pulled them from the P2P proto, else I'd fire one over.

@smeggy - I used that very pot in my 1st build & while taper is not ideal, it worked fine. Did replace it later w/BoM pot (as part of larger order).
Someone here did use that pot & wired its switch as on/off in CTH, forget who, but if you do this you are running A/C wires right across the board. And you'd be bringing A/C to *very* close proximity to low-level input within the pot. Wouldn't be surprised if you got some hum doing it.
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post #1002 of 2203
4/28/09 at 12:37pm
I used the larger hammond case, but still kept the input/output at the front with the pot, and let the AC live at the back.. Simple is better .. the more AC running around, the more noise you are going to get.. Keep the power switch at the back..
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post #1003 of 2203
4/28/09 at 1:43pm
I agree that bringing AC up front may cause noise issues due to the proximity. Though, my stance is different. Try it and find out. Don't build a case around it until you do. All my builds, for instance, run signal lines back to front, and I have no noise. As noted, others think it's not great, but it's my build.

Basically, try it and decide for yourself. Personally, I wouldn't do it on this amp, but that means nothing for anyone else. It may help others, should you find that it has no noise. One can even run a separate switch on the front, like full-sized amps. I don't think that'll cause problems, though I still wouldn't do it for other reasons.
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post #1004 of 2203
4/28/09 at 2:12pm
hmm. with no opamp the voltage voltage drops to 86v, which is nearer the mark for current draw......
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post #1005 of 2203
4/28/09 at 5:33pm
check the resistor values around the tube cathode servo and the cathode resistor (cathode resistor is probably correct)....R3, R4, R5, R6, R7, and R8. Opamp orientation?

I'm not sure how voltage is going *up* or might be possible if the operating point is completely different than what it should be. The servo sets up a voltage divider for the rail (the 2.3V you measured), feeds that into the positive leg as reference and uses a single ended non-inverting amp configuration to adjust the negative leg (which is the plate voltage with a divider).

What should be happening is that your default 86v will measure as ~2.6v (can check at the junction of R5 or R6. should drive down to the reference of ~2.3V.

Without the opamp in, measure the voltage at the cathode resistor, for reference.
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