2023 Monkeymatic Whitney (Deluxe Reverb)

[xtian]

Steve, my osc Rk is 3K3 (didn't have 2K7 on hand) and Rc is 25uF. And the three osc caps are all 0.02uF (I like the slower speed).

Also, where normal DR filtering is 32/16/16/16, mine is 47/22/22/22.

I'll try getting Rk closer to 2K7.

I may also try replacing the neon bulb with an LED.

[sluckey]

I don't think the roach is the problem. Sounds like your osc tube is starting but then dying. Might be helpful to replace the 3.3K/25µF cathode components with a 5mm red LED. This will give you a visual aid and it might just also fix the drop-out issue.

Might also help to use the standard Fender values for the osc caps, ie, .02, .01, .01. You can always modify later when it's running. Check the plate resistor too.

It would still be helpful if you post the layout.

[xtian]

Schematic and layout attached.

Here's some weirdness to consider: Voltages on V5A are correct, but voltages on V5B are NOT, and they depend on whether vibrato is engaged or not. With vibrato NOT engaged, V5B anode is 410v and cathode is 0v. With vibrato engaged, anode drops to 406v and cathode rises to 5v (according to schematic, voltages should be 345/17). When I disengage vibrato, cathode voltage drops slowly from 5v to zero.

I don't see how the vibrato switch could affect whether V5B is conducting.

[xtian]

I checked the V5B plate resistor: 100K.

I replaced V5A cathode 2K7/25u with a red LED. When vibrato engaged, I get 1.5v across the LED. It visibly pulses for a moment, then fades, though voltage stays steady.

Will try replacing oscillator caps with schematic values.

[xtian]

OK, Steve, stop worrying. I replaced C19/B and C19/C with 0.01u caps, and vibrato is working steadily now.

[sluckey]

I don't see how the vibrato switch could affect whether V5B is conducting.

When the vib FS is off (or unplugged) a big negative voltage from the bias supply is sent through R21 and R20 to pin 2 (osc grid). This turns the oscillator triode off.

That big negative voltage is also sent through R21 and R19 to pin 7 (driver grid). This turns off the roach driver triode.

[xtian]

My first cathode LED failed after a few minutes. I installed a higher-current, 10mm red LED, and it has lasted 30 min so far.

Everything is sounding great. I recorded a quick demo. Channel 2, with Reverb and Vibrato, is pretty much stock, with the exception of the "slower vibrato" mod. Channel 1 has a three-way Mid switch: stock (6K8), boosted (~50K), and lifted tone stack. Playing thru a Jensen N12K, audio from iPhone's mic.

[martin manning]

Sounding good!

[Reeltarded]

I was just on youtube listening to other amp and this popped up when I searched you trying to find another video..

SOUNDS AMAZING!!! Always great stuff!

[ViperDoc]

That sounds amazing, Aaron. Did you use a 2-spring long tank? Speaker sounds great too!

[xtian]

That sounds amazing, Aaron. Did you use a 2-spring long tank? Speaker sounds great too!

The tank is three-spring, long springs, and SHORT decay...can you believe it? Sounds LONG to me.

[ViperDoc]

The tank is three-spring, long springs, and SHORT decay...can you believe it? Sounds LONG to me.

Sounds great, just the right amount. Any more would be in the mush range if you ask me.

[xtian]

Mojotone cabinet arrived, along with my faceplates from Indcom.graphics. The cabinet is excellent--fine attention to detail, edges, and glue. Really nice. Very happy with this sexy package.

IMG_0350.jpg

IMG_0349.jpg

IMG_0348.jpg

IMG_0347.jpg

IMG_0346.jpg

[sluckey]

You build some really nice looking amps.

[pompeiisneaks]

You build some really nice looking amps.

Can't agree more, huzzah!

~Phil