Regulated Tube Power Supply Help

[littlerepairshop]

Hi there,

I recently acquired a Conway Electronic Enterprises Model PS-1 Regulated Power Supply. It is very very similar to the PACO B-12 but I think identical to the EICO 1030.

http://jlandrigan.com/files/EICO%201030%20schematic.pdf

Here are my observations.

The Bias supply seems to not be providing voltage from either the pos or neg terminal, but seems to accurately provide positive only voltage when measured between the pos and neg terminals.

The Heater supply works fine, as do all the other heater lines that feed the tubes inside. In fact all voltages out of the transformer seem good.

The Regulated supply does not appear to do anything.

The build quality is excellent and all the components are original (ie over 50 years old) so I figure I'll be swapping out the electrolytic and wax caps, but my understanding of this circuit is incomplete and if anyone has an idea of where I should I should begin I would be very grateful.

 

[rayma]

This is normal, the outputs are floating in this supply. It is a single voltage, not a bipolar supply.
Connect the polarity of voltage that you want to be grounded with a jumper to the ground post.

Odds are that it has had little use, so the capacitors could well be fine. Burn it in for a few hours
and use it normally until it actually needs work. It may go another 20 years without any service.

 

[littlerepairshop]

This is normal, the outputs are floating in this supply. It is a single voltage, not a bipolar supply.
Connect the polarity of voltage that you want to be grounded with a jumper to the ground post.

Odds are that it has had little use, so the capacitors could well be fine. Burn it in for a few hours
and use it normally until it actually needs work. It may go another 20 years without any service.

I'm not sure I follow. On the Bias supply you're saying it isn't bipolar? That seems not very useful.

On the Reg supply, referenced to ground I get about 6V on the neg and 4V on the pos terminal, with the output dialled all the way off. If I jump neg to ground suddenly I have -24V on the pos and if I jump pos to ground I have +24V on the neg side, again with the output dialled all the way off. Turning up the output does not increase the voltage.

Basically it is not working normally

 

[rayma]

The photo is poor, but there appears to be a white line (indicating a connection) between the bias positive output
and the negative regulated output. Measure between the negative regulated output and the bias positive.
Do not use ground for measurement, as it is not connected to anything unless you add an external jumper.
This is normal, many pieces of lab equipment are built this way.

 

[littlerepairshop]

The photo is poor, but there appears to be a white line indicating connection between the bias positive output and the negative regulated output. Measure between the negative regulated output and the bias positive.
Do not use ground for measurement, as it is not connected to anything unless you add an external jumper. This is normal, many pieces of lab equipment are built this way.

Yes that is correct, pos bias and neg reg are connected, so measuring between them is the same as just touching the multimeter leads together.
The ground lug is attached to the chassis, as is the ground wire on the power cord
Any advice for if the unit is NOT working as designed?

 

[littlerepairshop]

I included a link in the OP but I'll upload it here

 

[rayma]

Check all the tubes. Then measure all the internal node voltages wrt the negative regulated terminal.
The floating supply (blue leads, around 270VDC) could easily cause failure of the regulator to operate
properly, if it is not working. Look for an open resistor or a bad connection.

 

[littlerepairshop]

Check all the tubes. Then measure all the internal node voltages wrt the negative regulated terminal.
The floating supply (blue leads, around 270VDC) could easily cause failure of the regulator to operate
properly, if it is not working. Look for an open resistor or a bad connection.

Thank you, I appreciate your taking the time

 

[littlerepairshop]

Ok so the bias voltage is working fine when referenced to the reg neg. The 5AR4 seems to be only pulling 590V instead of 640V, and the screens of the 6L6's are seeing 209V instead of 265V, while the grids have -107V instead of -52V. I'm also reading around 2 meg of resistance across C3 the last 20uF 500V cap (out of circuit) before the reg voltage switch, which I think means it should come out.

 

[rayma]

Ok so the bias voltage is working fine when referenced to the reg neg. The 5AR4 seems to be only pulling 590V instead of 640V, and the screens of the 6L6's are seeing 209V instead of 265V, while the grids have -107V instead of -52V. I'm also reading around 2 meg of resistance across C3 the last 20uF 500V cap (out of circuit) before the reg voltage switch, which I think means it should come out.

Check the line voltage spec (117 VAC) and compare with yours, which could be different.
Try it on a Variac set to spec input AC line. Also capacitors just after a rectifier tend to go first
due to heating, and cause lower DC than when new. But, tube circuits can have 10% variation
without much harm. The CR1 could be bad/weak, as could C1A/B or R1.

 

[kward]

The 5AR4 seems to be only pulling 590V instead of 640V, and the screens of the 6L6's are seeing 209V instead of 265V, while the grids have -107V instead of -52V.

What was your voltage reference for those measurements? On the schematic you will notice that 0V is labeled as the voltage on the cathodes of the 6L6 tubes. In other words after the rectifier and 6L6 plates, all voltages listed are relative to the 6L6 cathodes, because the grid and screen voltages are biased up by the voltage on the cathodes (which voltage is user adjustable).

For an accurate (relative to the schematic) reading of those voltages quoted you need to measure with pos meter probe on the point you want to measure and neg meter probe on the 6L6 cathodes.

Now, you may still determine the HV supply isn’t working correctly, but you must do the measurements with proper voltage reference first before coming to that conclusion.