Philco 100 Century - UK Vintage Radio Repair and Restoration Discussion Forum

Vintage Tim · 7th Aug 2021, 11:31 pm

I have a nice Philco 100 in the throes of restoration but am now completely stuck with the FM tuner. It's a variable inductance type and the photos show the schematic and the tuner on the chassis and opened for inspection. The sliding cores move freely but it will only tune upwards from 100MHz whatever I do with the oscillator trimmer. The RF trimmer peaks up OK. I assumed that the capacitors across the oscillator coil have failed, but I can't seem get any response when temporarily patching over the existing C55 and C53. Testing is difficult without reassembling it into the can. Please can anyone suggest a solution before I give up and leave it AM only?

vinrads · 8th Aug 2021, 9:22 am

Hi Tim.

Are all the DC voltages correct on the UCC85? The HT feed resistors are prone to going high. Worth checking.

Mick.

Vintage Tim · 8th Aug 2021, 11:38 am

Thanks Mick, HT and heater voltages are OK. replacing the UCC85 makes no difference either.

vinrads · 8th Aug 2021, 12:50 pm

Does the osc trimmer have any effect I am thinking c54 worth bridging it , Mick.

Vintage Tim · 9th Aug 2021, 12:18 am

Hi Mick,
The osc. trimmer has very little effect on the tuning frequency but does seem to provoke some instability and "birdies" at low to minimum capacity. C54 is a pig to get at but I'll try bridging it. The Trader service sheet gives C51 and C52 8.2pf each, C53 14pf and C54 and C55 9pf each. If these capacitance values are correct then I wouldn't expect the trimmer to have that much effect on the frequency range, the oscillator seems about 12MHz high? What do you think?

vinrads · 9th Aug 2021, 9:12 am

I restored one of these recently ,and had trouble with a similar fault someone had soldered a twisted wire on the osc adjusting screw to earth ,I knew this was a bodge ,so removed it , to find the trimmer adjusted ok just a thought ! are the 10.7Mhz I.F's aligned ok. Mick.

Vintage Tim · 9th Aug 2021, 11:43 pm

It's beginning to seem like I've got to be brave enough to rebuild this horrible tuner, carefully reproducing the layout with new C's and R's. There are though only so many times it can be dismantled and reassembled for testing and then taken apart again because it still doesn't work, and the cramped wiring and hidden joints are not exactly an incentive!

I have a Mullard LP1179/2 tuner from a scrap R707, which will need a stable 7v supply but I think it might work to provide an FM IF output to the UCH81. It looks as if it would be possible to arrange the tuning drive to cope with its spindle pulley.

Not original, but with a big 270 ohm R to replace the UCC85 heater who'd notice?

This is the voice of desperation! Tim

Vintage Tim · 19th Aug 2021, 9:27 am

After reassembling the tuner having replaced C53 and C54 and some repositioning of possibly misplaced wiring, it's now tuning well at the top end of the band with good sensitivity. However... any attempt to tune below about 99MHz puts it into violent instability, with high frequency audio output resulting.
Still, progress, but another dismantling needed to trace the problem. It's got to be wiring positioning hasn't it?

Vintage Tim · 18th Sep 2021, 12:01 am

The solution has finally revealed itself, the instability was indeed due to stray coupling between the oscillator and the RF input amplifier. Following the alignment procedure in the Trader service sheet was producing too much gain! Detuning C49 in the RF amplifier away from the 94MHz peak specified suddenly started to improve things. Then I realised that C48, one of the ceramic tube and screw type of variable caps, was fractured, so I made a replacement using a slim paxolin tube with a small sleeve of brass. It came out at 10pf by some miracle! The aerial input transformer L2 had had no core when I first opened the case, but putting one in helped greatly in stabilising the circuit. So, by repeatedly going over all the adjustments to eliminate the feedback while keeping the gain up and the frequency calibration nearly right, I've finally got acceptable results.
Now to put it all back into the cabinet which has been beautifully restored by my beautiful beloved, and enjoy just looking at it. Can't plug it in: it's live chassis........

vinrads · 18th Sep 2021, 9:29 am

Well done perseverance paid off , Can't plug it in it's live chassis ! not sure what you mean. Mick.

Vintage Tim · 6th Oct 2021, 3:00 pm

Well Mick, that was a bit of sarcasm really. but I shouldn't expose anyone to a poorly insulated old AC/DC set where the chassis is directly connected to the mains. it could be of course connected to the live side by accident?

7th Aug 2021, 11:31 pm	#1
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Philco 100 Century I have a nice Philco 100 in the throes of restoration but am now completely stuck with the FM tuner. It's a variable inductance type and the photos show the schematic and the tuner on the chassis and opened for inspection. The sliding cores move freely but it will only tune upwards from 100MHz whatever I do with the oscillator trimmer. The RF trimmer peaks up OK. I assumed that the capacitors across the oscillator coil have failed, but I can't seem get any response when temporarily patching over the existing C55 and C53. Testing is difficult without reassembling it into the can. Please can anyone suggest a solution before I give up and leave it AM only? Attached Thumbnails

8th Aug 2021, 9:22 am	#2
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: Philco 100 Century Hi Tim. Are all the DC voltages correct on the UCC85? The HT feed resistors are prone to going high. Worth checking. Mick.

8th Aug 2021, 11:38 am	#3
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Re: Philco 100 Century Thanks Mick, HT and heater voltages are OK. replacing the UCC85 makes no difference either.

8th Aug 2021, 12:50 pm	#4
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: Philco 100 Century Does the osc trimmer have any effect I am thinking c54 worth bridging it , Mick.

9th Aug 2021, 12:18 am	#5
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Re: Philco 100 Century Hi Mick, The osc. trimmer has very little effect on the tuning frequency but does seem to provoke some instability and "birdies" at low to minimum capacity. C54 is a pig to get at but I'll try bridging it. The Trader service sheet gives C51 and C52 8.2pf each, C53 14pf and C54 and C55 9pf each. If these capacitance values are correct then I wouldn't expect the trimmer to have that much effect on the frequency range, the oscillator seems about 12MHz high? What do you think?

9th Aug 2021, 9:12 am	#6
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: Philco 100 Century I restored one of these recently ,and had trouble with a similar fault someone had soldered a twisted wire on the osc adjusting screw to earth ,I knew this was a bodge ,so removed it , to find the trimmer adjusted ok just a thought ! are the 10.7Mhz I.F's aligned ok. Mick.

9th Aug 2021, 11:43 pm	#7
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Re: Philco 100 Century It's beginning to seem like I've got to be brave enough to rebuild this horrible tuner, carefully reproducing the layout with new C's and R's. There are though only so many times it can be dismantled and reassembled for testing and then taken apart again because it still doesn't work, and the cramped wiring and hidden joints are not exactly an incentive! I have a Mullard LP1179/2 tuner from a scrap R707, which will need a stable 7v supply but I think it might work to provide an FM IF output to the UCH81. It looks as if it would be possible to arrange the tuning drive to cope with its spindle pulley. Not original, but with a big 270 ohm R to replace the UCC85 heater who'd notice? This is the voice of desperation! Tim

19th Aug 2021, 9:27 am	#8
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Re: Philco 100 Century After reassembling the tuner having replaced C53 and C54 and some repositioning of possibly misplaced wiring, it's now tuning well at the top end of the band with good sensitivity. However... any attempt to tune below about 99MHz puts it into violent instability, with high frequency audio output resulting. Still, progress, but another dismantling needed to trace the problem. It's got to be wiring positioning hasn't it?

18th Sep 2021, 12:01 am	#9
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Re: Philco 100 Century The solution has finally revealed itself, the instability was indeed due to stray coupling between the oscillator and the RF input amplifier. Following the alignment procedure in the Trader service sheet was producing too much gain! Detuning C49 in the RF amplifier away from the 94MHz peak specified suddenly started to improve things. Then I realised that C48, one of the ceramic tube and screw type of variable caps, was fractured, so I made a replacement using a slim paxolin tube with a small sleeve of brass. It came out at 10pf by some miracle! The aerial input transformer L2 had had no core when I first opened the case, but putting one in helped greatly in stabilising the circuit. So, by repeatedly going over all the adjustments to eliminate the feedback while keeping the gain up and the frequency calibration nearly right, I've finally got acceptable results. Now to put it all back into the cabinet which has been beautifully restored by my beautiful beloved, and enjoy just looking at it. Can't plug it in: it's live chassis........

18th Sep 2021, 9:29 am	#10
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,754	Re: Philco 100 Century Well done perseverance paid off , Can't plug it in it's live chassis ! not sure what you mean. Mick.

6th Oct 2021, 3:00 pm	#11
Vintage Tim Diode Join Date: Nov 2005 Location: Nottingham Posts: 8	Re: Philco 100 Century Well Mick, that was a bit of sarcasm really. but I shouldn't expose anyone to a poorly insulated old AC/DC set where the chassis is directly connected to the mains. it could be of course connected to the live side by accident?