Sound City 50 R

[louis]

Hi everyone !.......I just received a Sound City 50 R ,
The Sound City 50 R is the same as a SC 50 Plus but with a Reverb .

One of the spring is gone and also the two small holders on each side that holds them in place .
I dont have the two holders missing for the other spring ,wishe It could be repaired.

Also !......beside the fuse on the left in the back ,there is an input ,anyone knows what that one's for ?

There is also a trim pot near the preamp tube holder , ?

Anyone here has a spare SC black knob cap ?



Louis

[OldSchoolDave]

Hey Louis,

I am on a very SLOW internet connection at the moment and can't pull up your big pics. I would expect there to be a footswitch jack to engage the Reverb on that amp. Can you trace the wires from the "mystery jack" to the Reverb circuit?

Repairing that Reverb tank would be a challenge. The good news is, a quick google of "accutronics 8AB" reveals they're still producing tanks in that series. Some careful research might locate a modern replacement.

The trim pot appears to me to be for the power tube bias. Good to have some adjustment there.

Other than that, I can't be of much help.

Dave

[louis]

Hey Louis,

I am on a very SLOW internet connection at the moment and can't pull up your big pics. I would expect there to be a footswitch jack to engage the Reverb on that amp. Can you trace the wires from the "mystery jack" to the Reverb circuit?

Repairing that Reverb tank would be a challenge. The good news is, a quick google of "accutronics 8AB" reveals they're still producing tanks in that series. Some careful research might locate a modern replacement.

The trim pot appears to me to be for the power tube bias. Good to have some adjustment there.

Other than that, I can't be of much help.

Dave

Thank's Dave !!

I think you're right about the on/off Reverb switche , make's sence !....I found this on the Sound City Site,

Reverb In/Out
Available on some Mark 2, Mark 3, and some Mark 4 amps, these jacks provide the standard preamp loop functionality found on virtually all modern amplifiers, and are considered self-explanatory other than to say In = Return and Out = Send.

--------------------------------------------------------------------------------
Sensitivity Switch
In brief, and relatively speaking, the sensitivity switch, located on the rear panel of the Sound City 50 Plus Mark 4 and 120 Mark 4 amplifiers, makes the amp louder in position 1 and quieter in position 2.

The sensitivity switch affects the preamp by changing the cathode biasing point of the V3 ECC83 by means of switching a resistor in or out in series with the main biasing resistor of that stage.

"Cathode bias" raises the cathode voltage above ground by means of a resistor. The voltage drop on the resistor causes the voltage on one side of that resistor to be at a different potential than the the voltage on the other side of the resistor. The cathode is at a positive voltage above ground, and the grid is at ground level. Think of the cathode being at ground potential, with the grid being negative.

The sensitivity switch works by making this negative voltage less negative, with relation to the cathode, by means of taking one of the cathode resistors out of the circuit. Then if the bias voltage is smaller, the voltage from the previous part of the circuit seems greater and provides more amplification in the valve. On some SC schematics, this switch is labeled "GAIN."



I'll check for the Accutronic 8Ab , but I found a reverb tank taken out of a Hammond B3 ,
,do you think that it would work?.......same look and same lenght as mine.

here are the specs and what the auction says!,
You are bidding on a used Hammond/Gibbs Reverb Tank for Hammond Organs

I pulled this from an operational Hammond M111.

Input resistance is 1.1 Ohms; Output is 48.3 Ohms.
Has the letter "K" on inside. Measures 17" in length.

It is in working order.

Probably fits other applications however, I leave it to bidders
to determine if this item is correct for your application.

[OldSchoolDave]

I'll check for the Accutronic 8Ab , but I found a reverb tank taken out of a Hammond B3 ,
,do you think that it would work?.......same look and same lenght as mine.

here are the specs and what the auction says!,
You are bidding on a used Hammond/Gibbs Reverb Tank for Hammond Organs

I pulled this from an operational Hammond M111.

Input resistance is 1.1 Ohms; Output is 48.3 Ohms.
Has the letter "K" on inside. Measures 17" in length.

It is in working order.

Probably fits other applications however, I leave it to bidders
to determine if this item is correct for your application.

There are many different reverb tanks and most are NOT interchangeable. Input and Output Impedance are critical. I would not gamble on a tank without first knowing the values of the original. Other than the masking tape label, is there other identification?

Dave

[louis]

Thank's for the input Dave !

Did you finally see the pictures?

I bought an old tank that came from a Hammond M111 and I'm gonna
send everything to RGM451 here on the forum who his very skilled .
He will probably used the tank for parts to fix the other one .

I'll let you know !


Take care!.....................Louis