custom circuit -- proofreading needed --

[Enzo]

Ah, Saint Fubar, the patron saint of my shop...

[tedmich]

alternatively a 3-way NFB dampening switch or a dual resonance/presence pot could go there...or if you haven't already bought the OT maybe a triode/pentode/UL 3-way?
I guess if you actually use the STFU it'd be good to have

[rocksmoot]

Where are you at with this project? I'm very interested in this!

[mort]

Where are you at with this project? I'm very interested in this!

I'll probably be stringing it up this weekend. It's sat for a little bit collecting some mess around it.

[g1]

Ah... the ubiquitous "money shot" .

[nickb]

I think you might be just throwing money at it....

[tedmich]

looks good!

boy those fuse holders stick out pretty far, what PN are they?

[mort]

SH205 from AES/CE on the fuse holders.

[Wombaticus]

I'd add a, say, 220K resistor from the wiper of the bias pot to the top of the 25uF cap. That'll keep your power tube bias safe if the wiper of the bias pot should go bad or intermittent...

[The Dude]

I'd add a, say, 220K resistor from the wiper of the bias pot to the top of the 25uF cap. That'll keep your power tube bias safe if the wiper of the bias pot should go bad or intermittent...

Good point! I might even consider swapping the pot and resistor to ground positions (change values accordingly) so that if the pot goes wonky the bias -V goes higher instead of lower.

As an example only:

[Enzo]

I usually wire the pot as a variable resistor rather than as a pot (tie the wiper to one end) as you did. if the wiper fails it defaults to max voltage.

[Richard]

Learn something new every day. I'm so used to using the switch I feel weird just flipping on a solid state amp and playing. When I get around to my build I'll have to use a different way to mute the amp.

[mort]

Got some time today to finish up the wiring on this. The normal channel sounds great and there's ZERO unwanted noise/hum so that's great. The EF86 channel was weak though. I just did a quick B+ check before putting it away for the night and found ~400vdc going into the 220k resistor and like 13vdc coming out of it. On an AC15 schematic I have it shows 90vdc on the EF86 plate and tube data shows the plate rated for up to 250vdc. Should I just experiment with the dropping resistor or is there more to it than that?

[Malcolm Irving]

... The EF86 channel was weak though. I just did a quick B+ check before putting it away for the night and found ~400vdc going into the 220k resistor and like 13vdc coming out of it. On an AC15 schematic I have it shows 90vdc on the EF86 plate and tube data shows the plate rated for up to 250vdc....

Sounds like a wiring error or a wrong component value somewhere around the EF86. What voltages are you getting on the cathode, screen and grid of the EF86?

[Justin Thomas]

Check your component values - not just marked values, but out of circuit with a meter. Color codes can be misread, or misprinted... Maybe some a resistor is off by a factor of ten.

Less likely, the first time I built an EF86 stage, my socket was crap, and was throwing voltages way off. Had the same issue in the PI. So I don't use those sockets anymore. They were the ceramic two-piece ones, where the metal center portion holds them together. Bluh.

Justin