Silverface Deluxe loud

[shagual]

A good friend dropped off a deluxe reverb from (I guess) '79. Its got the line out & the volume boost push Pot.

I've got building experience with the blackface version but this one Silverface is extremely loud at low settings. I mean: in vibrato channel I measure slightly over 30 watts output when its on 3. Same counts for the normal channel

Bias of the 6V6s are on 21ma, B+ voltage is on 440-450.
I did notice the plate voltages of the preamp were way higher than the blackface versions, so I did change the 2.2K filter resistor to 10K -> All plate voltages and bias of the preamptubes (V1-V5) seem to be very close to the blackface area but didn't solve the early loud "problem"

Phase inverter
I guess the problem might be at the phase inverter
http://users.telenet.be/pierssens/SF/DSC00072.JPG
Pin1 voltage: 223DC
Pin 6 : 201DC
PIN3,8: 64DC

330K resistors at the grids
680 ohm resistorat the cathodes (there is 2.1DC over this resistor)


When modifying the phase inverter to Blackface specs will I have a smoother volume control?

Thanks for your input!

[Bruce / Mission Amps]

Is it using the correct 5U4GB rectifier?
I doubt it is making +30 watts... the most they ever really do is around 22-24 watts... you might be measuring a lot of distortion products mixed into the signal and your meter is adding it all together.

If you black face the phase inverter, make sure you don't use any coupling cap over 1500pF to 2200pF from the two 220K mixing resistors.
No, you wont have any smoother volume control by black facing the phase inverter.

[shagual]

Thanks Bruce,

its using a GZ34 rectifier.
I do measure the output the following way, input signal of 100mvac, dummy load of 8 ohm. I measure the maximum true rms ac, which is off course heavy distorted.

Problem is that my blackface gives this kind of output level when its above 8.5 , this silverface is already loud at 4 (more like all or nothing).

I'll go through a silverface and a blackface with a scope tomorrow.

[madkatb]

Any chance the volume pot is linear instead of audio taper?

[Amp Kat]

Any chance the volume pot is linear instead of audio taper?

Or even maybe a different value ?

[shagual]

all pots were fine, were never modified.

circuit was 100% original, only a dubble bias pot was installed

Did replace V2 with a 12AY7 and the amp sound so much better (better control on the volume), probably the original V2 was rather high gain.

A 12AT7 will probably give me the right sound & breakup

[Bruce / Mission Amps]

I'm pretty sure ALL the silver face Deluxe Reverb amps used a 5U4GB rectifier... and keep the tubes idle at around 9-10 watts each, regardless of what the actual B+ at the plates ends up being.
Don't use a 12AT7 in that amp for anything other then the reverb driver and phase inverter... it won't really sound right if you do.
A 12AY7 is OK, I guess, but the real tweak is to get the B+ voltage down around 410v-420v at the first main filter cap.

[shagual]

I'm not sure the powertransfo can handle a 5U4GB, it's already running hot. (PT is non original, 240 ac convertion done in the past).

B+ is 440dc, not dramatic. 6v6s are biased at 23mA

thanks Bruce!