Solartron SRS-152 - UK Vintage Radio Repair and Restoration Discussion Forum

BjornAudio · 27th Jul 2021, 9:33 pm

Hi Guys,

I have just acquired the above, the EL37 were only populated with 1 out of the 3, but that is not the issue.

I plugged it into the Variac and Bulb current limiter, and the bulbs glowed very dimly at 240VAC.

I measured the current and tested the caps on the LCR etc and all seemed well.

I plugged it into the mains and all was well, I could vary the voltage through the range and it was stable, but after around 10 minutes the fuse blew (3A).

I replaced the fuse and went back to the variac and current limited and the bulbs were glowing pretty bright.

I then tested for caps again, all good, and then tested the winding on the primary and secondary.

All was good except for the 400-0-400 and 670-520-360-0-360-520-570 were showing 470ohm from CT of the 400-0-400 and 670-520-360-0-360-520-570.

Looking at the schematic of the SRS-151 the CT are not common in the circuit, but I desoldered the hook up wires and there still existing the same 470ohm.

Reality is that the 400-0-400 is not a tap of the other as far as I can tell, but there is little info on this, plus I doubt Solartron would have changed the design so drastically.

My conclusion is that there is a short on the 400-0-400 to the other winding, which would also explain the time it took as this could have been small at first but as the current built it got worse.

Any help/advise/direction would be great, I have designed a new transformer and asked for quotes, I seriously cannot see any other issues and I have had the thing literally stripped to the chassis to clean it.

Thanks in advance

Björn

dave cox · 29th Jul 2021, 4:41 pm

Björn ,A reading of '470R' seems kind of low for a insulation breakdown and kind of high for a short circuit. Are you sure you are not reading a short in series with a winding ? And, its not clear if you disconnected all windings to make the measurement or just the center-taps ?

In case you have not already tried, I would measure from each tap on 1 winding to each tap on the other winding - with NO external connections - and look for the lowest reading.

I don't have a circuit diagram for this PSU, but unless there is some other cross-connection (in addition to a short in the TX) no current can flow!

HTH, dc

27th Jul 2021, 9:33 pm	#1
BjornAudio Diode Join Date: Jul 2021 Location: Salisbury, Wiltshire, UK. Posts: 1	Solartron SRS-152 Hi Guys, I have just acquired the above, the EL37 were only populated with 1 out of the 3, but that is not the issue. I plugged it into the Variac and Bulb current limiter, and the bulbs glowed very dimly at 240VAC. I measured the current and tested the caps on the LCR etc and all seemed well. I plugged it into the mains and all was well, I could vary the voltage through the range and it was stable, but after around 10 minutes the fuse blew (3A). I replaced the fuse and went back to the variac and current limited and the bulbs were glowing pretty bright. I then tested for caps again, all good, and then tested the winding on the primary and secondary. All was good except for the 400-0-400 and 670-520-360-0-360-520-570 were showing 470ohm from CT of the 400-0-400 and 670-520-360-0-360-520-570. Looking at the schematic of the SRS-151 the CT are not common in the circuit, but I desoldered the hook up wires and there still existing the same 470ohm. Reality is that the 400-0-400 is not a tap of the other as far as I can tell, but there is little info on this, plus I doubt Solartron would have changed the design so drastically. My conclusion is that there is a short on the 400-0-400 to the other winding, which would also explain the time it took as this could have been small at first but as the current built it got worse. Any help/advise/direction would be great, I have designed a new transformer and asked for quotes, I seriously cannot see any other issues and I have had the thing literally stripped to the chassis to clean it. Thanks in advance Björn

29th Jul 2021, 4:41 pm	#2
dave cox Nonode Join Date: Jan 2009 Location: Bristol, UK. Posts: 2,062	Re: Solartron SRS-152 Björn ,A reading of '470R' seems kind of low for a insulation breakdown and kind of high for a short circuit. Are you sure you are not reading a short in series with a winding ? And, its not clear if you disconnected all windings to make the measurement or just the center-taps ? In case you have not already tried, I would measure from each tap on 1 winding to each tap on the other winding - with NO external connections - and look for the lowest reading. I don't have a circuit diagram for this PSU, but unless there is some other cross-connection (in addition to a short in the TX) no current can flow! HTH, dc