Reverb Deluxe but not quite

[guile]

Dear fellow electron tinkers,
A long time ago I built my first tube amp, a Reverb Deluxe AB763 circuit.
Pictures: https://www.flickr.com/photos/115176149 ... 9230344990

I never play with reverb so I ordered a kit without the reverb part of the circuit, not knowing that the tone I was after is actually in the reverb channel (if I'm not mistaken).
The amp serves me daily, at home and in live situations and it never fails me, but the other day I heard how a Reverb Deluxe can sound. Lots of sag, very forgiving, sparkly, warm etc. My RD sounds okay and works fine but should be capable of much more. My question is if it were possible to make the amp produce more of the the magic that the original is capable of.
Tubes, biasing, speaker are fine btw.

I built some amps since then (Soldano SLO, 5E3 Tweed Deluxe), and lots of pedals, but I'm not a technician, more a sucker for nice gear, so please bare with me.
Thanks for any suggestions.

[xtian]

Please post a schematic that accurately represents YOUR amp, and start by measuring the B+ voltage at the anodes of each gain stage, and the power tube's anodes and screens, and report the bias.

Sometimes when you delete a portion of a Fender schematic (one channel, or the reverb, or tremolo) you reduce the load on the power supply, and this allows B+ to rise (higher headroom) and less sag. Adding resistance in the power string can get you back in the ballpark, so that's why I want to see your voltages.

[guile]

Thanks for your reply.

I added the schematic + layout: https://www.flickr.com/photos/115176149 ... 9230344990
It appears there is a a 220K resistor to compensate?

Could you please tell me what to measure exactly and where?
- B+ voltage at the anodes of each gain stage
- Power tube's anodes and screens
- Bias.

Thanks!

Love your builds btw

[xtian]

Measure B+ at the HT fuse; this is the power tube's plate voltage, within a few volts.

Measure B+ after the choke; this is the screen voltage.

Measure DC at pins 1,6,3,8 of each preamp tube.

Measure DC across the 1R bias sense resistors.

That 220K-to-ground resistor you point out drops half the volume going into the PI, but does nothing to address higher voltages. If you want more gain, remove it.

Thanks for the compliment!

[didit]

As noted, that's (more or less) just the "Normal" channel. And the "Vibrato" channel has quite different characteristics, even with reverb and tremolo off. Try out both channels on an actual DR, even if only on a re-issue. Then at least have clarity on what's being sought.

Best .. Ian

[guile]

Thanks very much.
Will get to it as soon as I can.

I will remove the 220k resistor and see what it does.

[TUBEDUDE]

Have you tried pulling the 5AR4 for a 5U4, or 5Y3?

[guile]

Have you tried pulling the 5AR4 for a 5U4, or 5Y3?

Yes, a 5U4.

[guile]

As noted, that's (more or less) just the "Normal" channel. And the "Vibrato" channel has quite different characteristics, even with reverb and tremolo off. Try out both channels on an actual DR, even if only on a re-issue. Then at least have clarity on what's being sought.

Best .. Ian

I'm looking for more sag, sparkle (les spikey/shrill highs), warmth, scooped, more forgiving. Fender clean, not tweed era (although fantastic), no crunch.

[guile]

Measure B+ at the HT fuse; this is the power tube's plate voltage, within a few volts.

Measure B+ after the choke; this is the screen voltage.

Measure DC at pins 1,6,3,8 of each preamp tube.

Measure DC across the 1R bias sense resistors.

That 220K-to-ground resistor you point out drops half the volume going into the PI, but does nothing to address higher voltages. If you want more gain, remove it.

Thanks for the compliment!

- Measure B+ at the HT fuse; this is the power tube's plate voltage, within a few volts.
378V

- Measure B+ after the choke; this is the screen voltage.
376V

- Measure DC at pins 1,6,3,8 of each preamp tube:
V1 Preamp tube (2AX7):
1 182v
6 170v
3 1.5v
8 1.5v

V6 Phase inverter (12AT7, not sure):
1 157v
6 145v
3 + 8 89,5v


- Measure DC across the 1R bias sense resistors.
I dont see any 1R resistors bias sense resistors:
22k: -32,7
68K: 120,5
12k: -25,8


That 220K-to-ground resistor you point out drops half the volume going into the PI, but does nothing to address higher voltages. If you want more gain, remove it.

Should I just clip it of or replace it with a lead so ground stays connected?
Not sure if I want lot's of gain because need headroom too for pedals.

[didit]

As noted, that's (more or less) just the "Normal" channel. And the "Vibrato" channel has quite different characteristics, even with reverb and tremolo off. Try out both channels on an actual DR, even if only on a re-issue. Then at least have clarity on what's being sought.

I'm looking for more sag, sparkle (les spikey/shrill highs), warmth, scooped, more forgiving. Fender clean, not tweed era (although fantastic), no crunch.

Voltage seem correct, even low, when compared to measurements shared in tale of two BFDRs. It appears you have 64uF at the DC power input, which is 2x original & doubtless helping stiffen things, thus perhaps not helping. Have you considered adding in an extra triode to create a "Vibrato" signal path?

Best .. Ian

[xtian]

I agree, voltages are acceptable.

1R bias sense resistors are shown on layout and schematic, connected to pins 8 of the power tubes. That's where you check the current flowing thru the power tubes at idle, that is, the bias.

No, don't replace the 220K resistor with a wire, that will get you zero volume.

As @didit said, 64uF reservoir is very stiff filtering.

[guile]

I agree, voltages are acceptable.

1R bias sense resistors are shown on layout and schematic, connected to pins 8 of the power tubes. That's where you check the current flowing thru the power tubes at idle, that is, the bias.

No, don't replace the 220K resistor with a wire, that will get you zero volume.

As @didit said, 64uF reservoir is very stiff filtering.

Thanks
I will measure the bias.

What will the extra gain yield (removing 220k resistor)?

So I should change the 64uf cap can?

[didit]

So I should change the 64uf cap can?

Too much work to change it out completely. Wire it up so you only use the first half.

[Lynxtrap]

What will the extra gain yield (removing 220k resistor)?

Like mentioned above, the 220K to ground cuts the gain in half at that point (gain factor 0.5). It's like you had a volume pot there and dialled out half the volume.
Removing the resistor means you'll hit the phase inverter with the full power coming out of V1B. You'll have considerably less headroom.

If you still want some attenuation, you could experiment with different values for the resistor to ground. Like, a 1M would give you a gain factor of about 0.8, etc.

More sparkle and less shrill highs is a tougher one. How does the bright switch work for you, if installed?
Just for experimentation, if you have components at home, I might try to install a very small cap in series with a resistor over that 220K resistor (not the one going to ground).
But the bright cap over the volume pot should pretty much do the same. If it's too much, put a resistor in series with that one.

What speaker do you use for this amp?