I've been fighting with a Westinghouse h-125 for weeks now and it seems to get worse and worse. It worked fine until I replaced all the capacitors and rubber wires and now I'm having a heck of a time with the oscillator among other things. I have checked and checked my rewiring with the schematic and only thing I can come up with is the old mica capacitors. I replaced them with ceramic disks, should I have used silver micas instead? I'm stumped..

Chris

Hi Chris

What problems are you having with the radio?

It's best not to replace mica caps around the oscillator circuit. Ceramic caps may not have close tolerance and can drift with temperature. You can buy silver mica cap replacements from AES and others.

Norm

:I've been fighting with a Westinghouse h-125 for weeks now and it seems to get worse and worse. It worked fine until I replaced all the capacitors and rubber wires and now I'm having a heck of a time with the oscillator among other things. I have checked and checked my rewiring with the schematic and only thing I can come up with is the old mica capacitors. I replaced them with ceramic disks, should I have used silver micas instead? I'm stumped..
:
:Chris

Norm,
Hopefully I can remember all the symptoms along the way. When I first rebuilt the chassis, I couldn't seem to get the alignment right, had all the vari caps in the i.f. xfmers unscrewed pratically all the way. I later discovered I was haunted with harmonics and got that situation under control. Then, reception was terrible and would only receive a very strong station without me holding the antenna loop. With the added capcitance of my hand, reception was very good but the oscillator would not adjust to scale and the antenna trimmer was once again almost completely unscrewed. I checked all connections at that time and ensured the loop antenna was not open, it measures 4 or 5 ohms. This is where I changed the mica caps and for some reason tossed the old ones in that mornings trash pickup. Symptoms as of today; I can inject modulated 455khz at the plate of the converter (12SA7) and tune my I.F.s with the exception of the primary of the first I.F. xfmr trimmer, it's screw is still very loose. The oscillator is obviously not running as a station a 670khz is all across the scale and loss of a strong station at 1240 khz.
I'm hoping my local electronics store will have silver micas in stock to replace the 47mmfs at the plate of the 12SK7 and grid of 12SA7 and see what develops.

Chris
:
: What problems are you having with the radio?
:
: It's best not to replace mica caps around the oscillator circuit. Ceramic caps may not have close tolerance and can drift with temperature. You can buy silver mica cap replacements from AES and others.
:
:Norm
:

Chris

By injecting a signal at plate of your 12SA7 you are adding capacity to the first IF Transformer. This may be why the screw is all the way out? Once the probe is removed IF Transformer primary will be out of adjustment. You should be able to inject a signal into another pin, try pin #8.

An oscillator not operating is a cause for one station being received, across most of the dial. Another cause can be IF's set too high in frequency. Any chance they are adjusted around 670? Pin #5 of your 12SA7 will be several volts negative when the oscillator operates. You should be able to hear the oscillator in a second radio tuned IF frquency above the station. (If radio under test is set to 1000, has an IF frequency of 455, the second radio should pick up a signal at 1455.)

Norm

:Hopefully I can remember all the symptoms along the way. When I first rebuilt the chassis, I couldn't seem to get the alignment right, had all the vari caps in the i.f. xfmers unscrewed pratically all the way. I later discovered I was haunted with harmonics and got that situation under control. Then, reception was terrible and would only receive a very strong station without me holding the antenna loop. With the added capcitance of my hand, reception was very good but the oscillator would not adjust to scale and the antenna trimmer was once again almost completely unscrewed. I checked all connections at that time and ensured the loop antenna was not open, it measures 4 or 5 ohms. This is where I changed the mica caps and for some reason tossed the old ones in that mornings trash pickup. Symptoms as of today; I can inject modulated 455khz at the plate of the converter (12SA7) and tune my I.F.s with the exception of the primary of the first I.F. xfmr trimmer, it's screw is still very loose. The oscillator is obviously not running as a station a 670khz is all across the scale and loss of a strong station at 1240 khz.
:I'm hoping my local electronics store will have silver micas in stock to replace the 47mmfs at the plate of the 12SK7 and grid of 12SA7 and see what develops.
:
:Chris
::
:: What problems are you having with the radio?
::
:: It's best not to replace mica caps around the oscillator circuit. Ceramic caps may not have close tolerance and can drift with temperature. You can buy silver mica cap replacements from AES and others.
::
::Norm
::
:

Thanks Norm,
Sounds like good tips for all radios, I'll hit the bench this afternoon with a new game plan! I called my local electronics store and they have 43pf and 51pf in silver mica, which way should I go to replace the 47pfs, high or low or hold out for a 47? Thanks!

Chris

Norm,
I found some 47pf mica caps on a parts chassis, transferred them to the "frig" and now have oscillator! Ran into the same aligment problem but figured out I was dealing with harmonics once again. Got the RFs properly aligned and now the little radio is back to the way it should be. Thanks for your help!

Chris