New Supro 1610rt No reverb

[pontiacpete]

First of all, are schematics available for these yet?

The reverb tank is a 8EF... type. There’s an AT7 for the drive and half (?)of a the next 12ax7 for the return. Tanks is good, cable checks out ok. There’s lots of high voltage on the AT7 pin 1 376v
pin2 245
pin3 250
pin6 376
pin7 245
pin8 249
changed both tubes
Do these voltages look good?

thanks

[Helmholtz]

Voltages don't look good. Might be a missing ground connection. What resistance do you measure between pins 3,8 and ground?
Do you know the input resistance of your DMM?

[Jon Snell]

With 245volts on the grids no and 250 on the cathodes is severe.
Schematic?

[pontiacpete]

There doesn’t seem to be a connection to ground on pins 3and 8.
I don’t know the input resistance of my meter. It’s a fluke 175

[pontiacpete]

Trying to upload a photo.

[pontiacpete]

here

[Helmholtz]

There doesn’t seem to be a connection to ground on pins 3and 8.
I don’t know the input resistance of my meter. It’s a fluke 175

The tube needs to see a resistance in the k range between cathodes and ground. Find the cathode resistor, check it and verify that one end connects to ground and the other to the cathodes.
I also suspect that the grid leak resistor has lost its ground connection while still being connected to the lower end of the cathode resistor.
Especially check for broken copper tracks near the eyelets.

Does the picture show the cathode resistor? What does it measure? Use your continuity tester to find all components it connects to.

Input resistance/impedance of the Fluke 175 is 10M for DCV and ACV. Always good to know.

[pontiacpete]

The open resistor is connected to pi’s 3 and 8.
I thought it might be 4.7k but that caused one of the dropping resistors I n the power supply to smoke. So I looked up the color codes(should have don’t that first damn metal film resistors) and now I’m using a 47k resistor on those cathodes and the reverb is working. This brought the voltages down about 20-30v on all the pins I gave measurements before.
Does this sound correct or expected?

[Jon Snell]

The resistor in the photo is a 4.7k, I would fit a 4.7k resistor. The type is immaterial as long as it is half watt in power or more.

[Helmholtz]

The resistor in the photo is a 4.7k, I would fit a 4.7k resistor. The type is immaterial as long as it is half watt in power or more.

It's 47k (5-ring code). But its value is unusually large for a rev. driver cathode resistor

[Helmholtz]

The open resistor is connected to pi’s 3 and 8.
I thought it might be 4.7k but that caused one of the dropping resistors I n the power supply to smoke. So I looked up the color codes(should have don’t that first damn metal film resistors) and now I’m using a 47k resistor on those cathodes and the reverb is working. This brought the voltages down about 20-30v on all the pins I gave measurements before.
Does this sound correct or expected?

Please post all tube pins' voltages.
Is the 47k the only cathode resistor, i.e. does it go directly between cathodes and ground?
Still wondering what made the grid voltage go so high.

[pontiacpete]

The 47K is. the cathode resistor to ground for pin 3 and 8.
The voltages are
Pin 1. 338
pin 2. 225
pin 3. 225
pin 6. 338
pin 7. 222
pin 8. 222

reverb works really well.

thanks

[Helmholtz]

The 47K is. the cathode resistor to ground for pin 3 and 8.
The voltages are
Pin 1. 338
pin 2. 225
pin 3. 225
pin 6. 338
pin 7. 222
pin 8. 222

reverb works really well.

thanks

Voltage values are still confusing (without a schematic). Incredibly high grid and cathode voltages. As the grid voltage didn't change much, it must be fixed biased.

Pin 2 and 7 voltages should be identical and one or two volts lower than pin 3,8 voltages.

Does the circuit have a reverb transformer (or do the plates (pins 1,6) connect directly to a supply node)? If not, where does the reverb tank input connect to? Is there a coupling cap that connects to the cathodes?

[pontiacpete]

Here’s a picture of the drive it connects to that 200 ohm resistor

[Helmholtz]

Here’s a picture of the drive it connects to that 200 ohm resistor

Sorry, I can't work like that. Please answer all of my questions. I can't identify resistor code colors in the picture nor can I read the circuit from a single side only. You have the amp and your meter.

I suppose that the amp uses a very uncommon cathode follower circuit to drive the reverb input via a coupling capacitor.