1950s Philips Radio Issues

[vortalexfan]

Greetings Everyone, I'm currently working on a 1950s Philips Model B6X15A/70 AM/SW HiFi radio that seems to have some weird issues.

Issue #1 that this radio is having problems with is extremely scratchy tuning in all tuning bands, which I thought it was because of dirt and dust trapped in the tuning condenser but when I cleaned it out it was still scratchy sounding when you tuned through the various tuning bands.

Issue #2 that this radio is having problems with was that when I got this radio the tuner was dead silent when I got it and it was dead silent in all of the different tuning bands, so I went and tested all of the tubes and all of the tubes tested fine except for the EBF89 tube which tested shorted in all 3 sections of the tube, so I had ordered a new EBF89 over at AES, and I installed that tube and the Radio worked great for about 5 minutes and then it went dead again.

I looked at the undercarriage of the radio to see what kinds of caps there were underneath and there weren't any paper caps underneath they were mylar (or some similar material) capacitors that don't fail as easily as the old paper caps that we used to use here for many years did, the filter caps are still good on this thing yet, which is what's throwing me for a loop as to why the EBF89 tube would be failing like it did.

Any ideas as to what might be going on with this radio?

Thanks.

[Electronic M]

Sixty year old mylar caps while usually good aren't infallible. If that tube has a DC blocking cap coupling signal to its grid and the cap went leaky the tube could be biased to conduct too hard and fail (measuring the grid bias and comparing to the schematic will tell you if this is happening).

Tubes that have been subjected to mechanical shock can sometimes just drop dead out of nowhere and that is also a possible explanation.

[vortalexfan]

Originally Posted by Electronic M

Sixty year old mylar caps while usually good aren't infallible. If that tube has a DC blocking cap coupling signal to its grid and the cap went leaky the tube could be biased to conduct too hard and fail (measuring the grid bias and comparing to the schematic will tell you if this is happening).

Tubes that have been subjected to mechanical shock can sometimes just drop dead out of nowhere and that is also a possible explanation.

Well I replaced the only capacitor that was associated with the EBF89 tube socket and still no dice (the replacement tube is still good, no shorts or anything and I tested the original capacitor and it still tested fine yet.)

Turning the tuning knob in all band modes is still producing a noisy crackly, scratchy noise when tuning across the dial, even though I blew a ton of crap out of the tuning condensers with some compressed air, and I even cleaned it out on top of that with some CRC QD Electronic Cleaner, and still no dice on the noisy tuning.

I tested the rest of the tubes in the radio (an ECH81, an ECC83, an EL84 and an EL86 and an EZ80 tube and the tubes tested fine, no shorts or anything, I even cleaned the band switching buttons with contact cleaner (the same stuff I used on the tuning condenser above) and still not getting anything, no reception, or audio or anything just a hissing noise and the crackling, scratching noise out of the tuner and thats it.

I'm at a loss here for what else to look at on this radio to get it working.

Also I noticed on the ID tag it says that its designed for 50 Cyc. A. C. Rather than 60 Cyc. AC, could that cause some issues with this radio not working correctly?

[Electronic M]

You may want to shine light through the tuning cap while turning it. Sometimes a plate gets bent and rubs and that can cause crackling and loss of reception.

Generally speaking a working 25Hz or 50Hz radio or TV will work as good or better powered at 60Hz...The power transformer will run cooler and the filter caps will be slightly oversized for 60Hz and thus filter hum better.

[vortalexfan]

Originally Posted by Electronic M

You may want to shine light through the tuning cap while turning it. Sometimes a plate gets bent and rubs and that can cause crackling and loss of reception.

Generally speaking a working 25Hz or 50Hz radio or TV will work as good or better powered at 60Hz...The power transformer will run cooler and the filter caps will be slightly oversized for 60Hz and thus filter hum better.

Ok, I'll check the tuning condensers when I get off from work, and see if there are some bent plates.

[zeno]

First new tubes sometimes are bad or go bad soon.
Second a tube tester is NOT 100% especially when at high freqs.
If the EBF89 is the audio out find the G1 pin ind follow that back to
the driver. there will be a cap between the driver plate & output G1.
Change it.
For the tuning noise check the previous tips. Also there is a way the
shaft gets grounded, clean that real good. On TV UHF tuners that
was a big problem.

73 Zeno
LFOD !

[vortalexfan]

Originally Posted by zeno

First new tubes sometimes are bad or go bad soon.
Second a tube tester is NOT 100% especially when at high freqs.
If the EBF89 is the audio out find the G1 pin ind follow that back to
the driver. there will be a cap between the driver plate & output G1.
Change it.
For the tuning noise check the previous tips. Also there is a way the
shaft gets grounded, clean that real good. On TV UHF tuners that
was a big problem.

73 Zeno
LFOD !

EBF89 is not the output tube, its in the tuner stage.

There is something bizarre I've noticed about this radio, it has two tuning condensers, a smaller one and a larger one, the larger of the two is super loose on the chassis (as in you can wiggle it back and forth with your hands loose) and I checked the mounting screws to see if they were loose and they were as tight as they could get, and I checked the grommets and they weren't melted or deformed or anything. would the main (large) tuning condenser being loose cause some issues with a noisy tuner?