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Post by DHockey on Sept 14, 2022 7:51:28 GMT 12
Hi John
I restored a Philips 594 some time ago, it was also a challenge! It had an AGC fault that was caused by B+ leaking across the wave change switch and onto the AGC bus. I ended up having to remove a section of the switch to remove some carbon tracking.
The audio driver transformer in the 141 is a step down type unlike a lot of other audio driver transformers due to the class B output stage requiring some power to drive it. I don't know what the turns ratio of the original was, it had been replaced by a Beacon Radio one with a ratio of 3:1 1/2 secondary. This didn't sound very good, the audio was a bit weak with some distortion.
I had a Hammond 124E transformer lying around and I ended up using this connected backwards. The dual secondaries were connected in series and became the new primary with about 135K ohms impedance. The original primary (now secondary) is 15K impedance. This gave a turns ratio of about 6:1 1/2 secondary. This sounded much better, plenty of volume and no noticeable distortion.
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Post by Philconut on Sept 14, 2022 9:07:52 GMT 12
Yes a difficult set all around really what with having to disconnect the dial to get it out of the cabinet but it does sound well. I have foregone the SW options. I'll have another go at it today. I have spent an inordinate amount of time on this set. Thanks for the transformer info. I'll ad it to my collection & see if it helps.
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Post by Philconut on Sept 16, 2022 8:38:36 GMT 12
A challenge indeed. I have, finally, traced the problem to a faulty padder trimmer. It measured 4.3k ohms across the terminals! Who would have thought of this. It's the first time I have come across this fault ever. Once again difficult to extract. I had to take it apart and completely clean it. Now I have to readjust the oscillator coil. Oh well, I'll know where to look next time. Hang on ......there won't be a next time for one of these monsters!!
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Post by DHockey on Sept 20, 2022 11:06:00 GMT 12
Glad you finally found the fault. I can't remember ever coming across a faulty trimmer! They couldn't be in a worse place in the chassis in terms of access.
For all its servicing difficulties, I'm quite partial to the Philips 594, I like the look of them and the unusual dial with the glass pointer. They are a good performer too when serviced.
By the way, I mentioned a Beacon Radio driver transformer in my earlier post. The type code for these is "D01" and the Beacon catalogue lists it as class B driver transformer for a 6N7
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