Supro 1622RT No reverb

[ca7922303]

MOD 4FB3A1B tank output(219 ohms), input(198 ohms). Are these readings right for this tank? Thanks

[The Dude]

If those are DCR readings and if you're asking if they are right for that tank, yes they look about right. If those are not DCR readings or if you're asking if it's the right tank for that amp, that's another story.

[Jon Snell]

Your 4FB3A1B has actually has impedances of;
Input 1.5k
Output 2.5k
Long Delay and mounts horizontally spring side open and facing down.

If you have DC resistance readings, then unless the springs are missing, it should be OK.
A schematic would help.

[ca7922303]

Your 4FB3A1B has actually has impedances of;
Input 1.5k
Output 2.5k
Long Delay and mounts horizontally spring side open and facing down.

If you have DC resistance readings, then unless the springs are missing, it should be OK.
A schematic would help.

Found bad RCA cable, replaced with new ones. Getting same dcr readings as before at reverb tank with new cable connected but no reverb.

[g1]

Disconnect the cable at tank 'output'. Turn up reverb and volume and touch the tip of that cable. Do you get a hum when you touch it? If not, try the same with the cable at the other end of the tank.

[ca7922303]

Disconnect the cable at tank 'output'. Turn up reverb and volume and touch the tip of that cable. Do you get a hum when you touch it? If not, try the same with the cable at the other end of the tank.

Getting hum from output cable. Reverb control affects volume of hum, volume pot has no affect on hum. Hear reverb when bumping tank, but no reverb with instrument installed, amp works good otherwise.

[ca7922303]

Getting hum from output cable. Reverb control affects volume of hum, volume pot has no affect on hum. Hear reverb when bumping tank, but no reverb with instrument installed, amp works good otherwise.

Except for one of the 6973s is red plating.

[ca7922303]

Except for one of the 6973s is red plating.

:2250 output/1475 input ohms is what the mod website shows for this tank, I'm getting 219/198 ohms.

[Enzo]

The MOD web site is telling you the IMPEDANCE of the reverb coils, your meters measure the DC RESISTANCE of the coils.

[g1]

Those resistance readings are correct for those impedances.
The red-plating tube is a separate problem. Swap the 6073's around and see if the same tube red-plates in the other position. If so, it needs to be replaced.
How many preamp tubes and what type are in this amp?

[ca7922303]

Those resistance readings are correct for those impedances.
The red-plating tube is a separate problem. Swap the 6073's around and see if the same tube red-plates in the other position. If so, it needs to be replaced.
How many preamp tubes and what type are in this amp?

4-12AX7s, 1-12AT7, 2-6973s

[ca7922303]

4-12AX7s, 1-12AT7, 2-6973s

Moved 6973, red plating moved with tube.

[Jon Snell]

I would fit a new matched pair of 6793s and check the bias to stop damaging the valves and causing hum.
(The 6793s were designed by RCA in 1957 and their primary use was to drive a pair of KT66s in a leslie cabinet amplifier.)
Schematic?
Edit; still cannot find schematic.

[Enzo]

What model did that? I know some two channel amps used 6973 for the small speakers and 6550 for main speaker.. Like this one:

http://www.captain-foldback.com/Lesl...matics/251.GIF

or

http://www.captain-foldback.com/Lesl...ics/51_51C.GIF

We also used a lot of them in Seeberg juke box amps of the era. Stereo amps, the small size of the tube took up less space.


I don't recall 6973 driving a larger pentode.

[Enzo]

Here Jon, you might find this useful, a collection of Leslie schematics.

http://www.captain-foldback.com/Lesl...schematics.htm