Hi there.

I'm still working on my Calstan radio and have just replaced the rectifier tube.

As I wound the voltage up I noticed that the rectifier was brighter than I expected. I measured the voltage across the rectifier filament as 6V which didn't seem right. I rang Neil at the valve store for a second opinion

We determined that that was a bit high so I wound down the variac to get 5V on the rectifier and tried to figure out what was happening. At the same time I measured the filament and HT voltages on the other tubes and it was now down around 4V and the HT had dropped to lower than required.

Could it be that the filament windings have been mixed up I thought.

I'd pulled them away while I took out the transformer to clean the chassis so I wondered if I had been stupid when I put it back.

I double checked the pictures I took before I touched it and it was exactly as I had received it.

I then carefully looked at the transformer and indeed it seems that the windings have been swapped.

From the way the wires from these windings have been cut to length and wrapped around components on their way to their destination it seems that this has been the situation for a very long time.

A couple of questions to the brains trust.

Have they seen this before. Is this likely to have been a production mistake or a later technician.

How long would it have run with this configuration.

Not sure what you mean in this context by windings being swapped. Swapped with what exactly? Can you be more specific.

GTC:

What I'm trying to say here is that the rectifier filament was fed with 6.3V and the other valves were fed with 5V.

Peter

OK, got it. Never seen such a thing personally, but hard to believe it would have come out of the factory in that condition. I guess anything's possible.

Definitely possible. Could even have been a mix-up when the transformer was wound.

Factories normally only did functional testing and the operators may not have been as clued in as you and I are.

Back in the 90s we once had a batch of product go out with 220v mains transformers instead of 240v. Would work just fine until you drove the amplifier a bit hard for a while, when the over-temp shut-down would come in.

Perhaps the only way to sort this is the history of the radio if known. Hard on rectifiers? Never a good performer?

Hi Peter,

I usually take a 'staged' or 'modular' approach to firing up any electronic stuff ... eg. I would probably disconnect the power supply completely from the rest of the radio ... power rails (B+), all filament windings etc ... so that any faults in the power supply that I might have missed during testing don't cause further harm. Then add Heater circuits, then DC power circuits, then re-install valves .....

If I do not know the history of the radio, it is never powered. Sometimes one will come in for repair that is barely working they can be exceptions to powering, but that is especially dependant on the condition of the mains, or battery side, which will be checked. Several mains sets have come in and one wondered at the time as to how they survived unplugging it?

The mains (side valve sets) should be tested with the Rectifier out (minimum) but, shorts are not uncommon secondary side, so that sort of thing should be looked for. If you leave things connected put a volt meter on the secondary.

Normally the winding's running heaters and filaments are solid and thick due to the current & a voltmeter should also sort them by the open circuit voltage.

Marc

Ian Robertson: There are some very faint markings on the transformer and it seems that the windings on the transformer are correct. I disconnected everything and measured the voltages. 6.3V went to the rectifier and 5V went to the rest of the valves. I took some of the advice above and the windings are connected to the incorrect places in the radio. The length, path and stiffness of the leads indicates that they have been that way for a long time. I've had to extend a couple of leads to get them connected to the correct location.

I've got some valves on order so I'll report back later.

Thanks again for your help. I'll add your suggestions to my future endevours.

Peter

If the rectifier is 5Y3 or #80. They are 5V filament valves Also note that the filament winding of those must never go to ground.

I would expect all other valves to be prefixed with six eg 6F6, 6V6........ The six is normally the voltage, but never take that for granted as number valves like #80, #58, UX201A and some starting with 7 & others do not do that.

If you continue repairing do acquire a valve data book, for reference on the valve, or look on Franks electron tube pages http://www.tubedata.info/ ... Always handy

Marc

Marcc: This is the cohort of tubes in this radio.

ECH35
6SK7GT
6SQ7GT
6V6GT
5Y3G

I've sent them off to Neil at The Valve Store for testing.

I should get the results in a few days.

I know from what I've done that the original 5Y3 is dead. Given the filament issue that's not surprising.

I've rewired the radio wrt the filaments and have tested the voltages without tubes and its all looking good now.

Thanks

Peter