Tel Ray Ad N Echo 1001

[mort]

Working on this unit and the effect doesn’t work presumably from a lack of oil. The correct oil has been ordered and will address that later.

The unit itself is passing weak, poorly distorting guitar signal and I’m currently trying to troubleshoot that. Here are some observations so far, based on this drawing: https://jray1.tripod.com/images/TelRay_Ad_N_Echo.gif

PT has been replaced with a Hammond 269JX and its heater taps (no CT) have been connected to the heater with the DC supply still in place on pin 4. (Would pin 5 in the drawing be originally attached to ground?)

The diode rectifier is currently a 4 diode full wave (2 diodes in series with each leg of HT and first filter. I’ll add a photo shortly. The drawing shows a 2 diode half wave on one leg. Could this be causing some sort of issue or would either style rectifier work fine in this application?

The first 10k dropping resistor has been changed to 2 10k’s in series and 2 10k’s in series have been added between node A and pin 1. I don’t see this being a problem necessarily, but felt it worth mentioning.

In summary, I’m asking if pin 5 should be tied to ground and the AC supply removed altogether, and what should be done with the rectifier?

[g1]

Schematic link is a dead end tripod thumbnail for me.

[mort]

….

[mort]

And here’s the rectifier.

[mort]

Ok so I tried disconnecting the PT heater supply and connecting pin 5 to ground. The filament would not work. So then the PT supply was put back on pins 4 & 5 and removed the DC supply, and added a virtual CT, which restored the clean signal through the circuit…. mostly.

Now the signal is full and clean but there’s a moderate to heavy hum. The screen pot is the only control that has any bearing on the hum but it also diminishes all signal if set too high or too low. It has to be in juuust the right spot for the guitar signal to sound its best.

2 readings seemed a little suspect… it’s getting -.3v on the input grid and the heater voltage is 7.4vac. Not sure how negative voltage can be present on the input… thoughts?

[Helmholtz]

PT has been replaced with a Hammond 269JX and its heater taps (no CT) have been connected to the heater with the DC supply still in place on pin 4. (Would pin 5 in the drawing be originally attached to ground?)

In summary, I’m asking if pin 5 should be tied to ground and the AC supply removed altogether, and what should be done with the rectifier?

Heater pin 5 must not be grounded. Heater supply is floating on HV (supply B), aka heater elevation.

A well designed full wave rectifier might be an improvement as it allows for lower ripple/better filtering.

I would start with measuring circuit voltages (supplies, tube cathodes and plates).
That will show if tubes are operating properly.

[mort]

Heater pin 5 must not be grounded. Heater supply is floating on HV (supply B), aka heater elevation.

A well designed full wave rectifier might be an improvement as it allows for lower ripple/better filtering.

I would start with measuring circuit voltages (supplies, tube cathodes and plates).
That will show if tubes are operating properly.

I’ve heard the term elevated heaters but don’t know how that works or how it could work with only one wire. Any help with that would be appreciated.

pin 1 - 322vdc
pin 2 - 53 vdc
pin 3 - 50.7 vdc
pin 4/5 - 7.4vac from PT
pin 6 - .57vdc
pin 7 - -.3vdc
pin 8 - 17.1vdc
pin 9 - 0vdc

[Helmholtz]

I’ve heard the term elevated heaters but don’t know how that works or how it could work with only one wire. Any help with that would be appreciated.

Well of the course the heater needs a 6.3V+/- 10% supply between pin 4 and pin 5, typically from a separate heater winding on the PT, not shown in this incomplete schematic.

Regarding heater elevation, see here: http://valvewizard.co.uk/heater.html

Will look at the voltages later.

[Helmholtz]

What is the "B" supply voltage?

Negative voltage at the input grid is caused by relatively large grid leak current. Is the grid leak resistor good?

Heater voltage is too high and should be lowered.
Does the PT use the black 125V primary tap?

https://www.hammfg.com/files/parts/pdf/269JX.pdf

[mort]

B+ is 409v

grid leak resistor is within spec and is 470k in this machine whereas the drawing shows 680k.

This PT does not have the primary option listed on the specs you linked. It just has 2 black leads rated at 115v.


Oh and thanks for the valve wizard link. I had seen the dc supply on top of the AC supply of the heater and immediately thought it was a mistake. I have a better understanding of that now.

[Helmholtz]

B+ is 409v

Something is wrong here. According to schematic "A" voltage must be higher than "B" voltage.
As point "A" voltage should connect to plate pin 1 measuring 322V, point "B" voltage should be lower than that.

This PT does not have the primary option listed on the specs you linked. It just has 2 black leads rated at 115v.

Pity, as using the 125V tap would lower your voltages by around 10%.

[mort]

My mistake, I thought you were asking B+, as in directly after the rectifier.

The “B” node has 344vdc.


I just put back the 470k and .047uF at pin 4 and it reduced the humm a bit. Perhaps the absence of a CT or virtual CT was the only mistake as far as the heater is concerned.

[Helmholtz]

The “B” node has 344vdc.

That's still above the voltage at node A. As said, B voltage should be lower than A voltage acc.to schematic. Are the nodes interchanged?

I just put back the 470k and .047uF at pin 4 and it reduced the humm a bit. Perhaps the absence of a CT or virtual CT was the only mistake as far as the heater is concerned.

The best way to minimize heater hum is a humdinger pot with the wiper connected to the elevation DC voltage.

But 344V is way too high for heater elevation. Vhk limit of the 7199 is +100VDC.
So you should lower the voltage by wiring a 100k resistor across the 0.047µ cap, i.e. from the 470k resistor to ground.

Do you have a scope?

[mort]

That's still above the voltage at node A. As said, B voltage should be lower than A voltage acc.to schematic. Are the nodes interchanged?

Easy to miss but this was noted in the 1st post

“ 2 10k’s in series have been added between node A and pin 1”

The best way to minimize heater hum is a humdinger pot with the wiper connected to the elevation DC voltage.

But 344V is way too high for heater elevation. Vhk limit of the 7199 is +100VDC.
So you should lower the voltage by wiring a 100k resistor across the 0.047µ cap, i.e. from the 470k resistor to ground.

Do you have a scope?

Here’s something I don’t understand about the DC going to pin 4. There are 3 470k resisters being fed by B. One of them drops the voltage to 50 something volts going to pin 2. One of them drops the voltage to around 120v going to the screen pot. The 3rd feeds pin 4 but there’s no DC voltage present on pin 4 in reference to ground. I’ve replaced that resistor already because it was out of spec but it didn’t change the voltage reading. Do I reference from somewhere else besides ground to see how much dc pin 4 is actually getting?


Here’s a fresh set of voltages after having replaced the DC supply to pin 4.


mains - 123vac
leaving rectifier - 407vdc
A - 343vdc
B - 327vdc
Pin 1 - 312vdc (20k dropped from A)
Pin 2 - 56vdc
Pin 3 - 49vdc
Pin 4/5 - 7.4vac
Pin 6 - .53vdc
Pin 7 - -.33vdc
Pin 8 - 16.5vdc
Pin 9 - 0vdc

[Helmholtz]

Easy to miss but this was noted in the 1st post

“ 2 10k’s in series have been added between node A and pin 1”

That text is not clear at all. Where is node B?
Please post a drawing of your actual power supply wiring with voltages.

The 3rd feeds pin 4 but there’s no DC voltage present on pin 4 in reference to ground. I’ve replaced that resistor already because it was out of spec but it didn’t change the voltage reading. Do I reference from somewhere else besides ground to see how much dc pin 4 is actually getting?

I suppose you grounded some point of the heater circuit. With DC elevation you can't do that as it will kill the DCV.
When you elevate pin 4, you can't use balancing resistors or ground the heater CT.

Here’s a fresh set of voltages after having replaced the DC supply to pin 4.
A - 343vdc
B - 327vdc

How come now node A voltage is higher than node B voltage?