No reception between 800 and 1200 KHz. - UK Vintage Radio Repair and Restoration Discussion Forum

capbuster · 22nd Apr 2010, 3:04 pm

Hello . My set plays but after about 25 minutes quits receving from around 800 to 1200 on the dial. No for sure all resisters are good all caps are new tubes just purchased them. And antenna coils check out. Seem like something getting hot cutting out . Does it quick not gradual . Philco model 111 Iknow i brought this up before but can not figure this out.

Thanks Denver.

julie_m · 22nd Apr 2010, 3:42 pm

Is the local oscillator running when the set goes quiet?

OErjan_S · 22nd Apr 2010, 3:54 pm

if this was me I would check the tuning capacitor, there might be something shorting it, dust, a stray bead of solder/wire or even a bent vane.

capbuster · 22nd Apr 2010, 4:02 pm

The oscillator is running . I watched all the valves while running. I cleaned the tuning condenser good . Could it be one of the mica caps ? If so which one would it be ?Most reading i done said leave these alone.

newlite4 · 22nd Apr 2010, 4:39 pm

This appears to be a very complex set with 11 valves, it is also 80 years old. Faultfinding is likely to be difficult. Try putting the original RF amp and oscillator valves back in and see if that improves things. New old stock valves can come with faults so it is worth checking this.
Neil

julie_m · 22nd Apr 2010, 4:57 pm

You won't be able to tell whether the oscillator has stopped just by looking at the valves. Instead, use this method:

Get a known-working radio (we'll call this "set 2" and the unknown "set 1"; it's easiest if set 2 is a battery portable). Tune set 2 to a weak station near the top (many kHz, few metres) end of the MW band and place near to set 1, as close as possible to the frequency changer valve. Tune set 1 slowly up the MW band. At some point, set 2 will go quiet as the LO in set 1 (which is equal to the tuned frequency plus the IF; the IF usually being about 470kHz) swamps the signal.

If the oscillator in set 1 stops, set 2 will burst back into life again.

capbuster · 22nd Apr 2010, 5:47 pm

I will try this . Let you know tomorrow have to get to work now .
Thanks and thanks Capbuster.

capbuster · 23rd Apr 2010, 1:24 am

Ok that is one neat ideal. It worked good the portable set would quit when tuned to same . But soon as it got warmed up good it quit oscillating .
I have ten #27 valves . Tried all of them in set surely all are not bad.
What else would cause the set to quit oscillating. PUZZLED. Reason i have ten #27 valves maybe first five were bad. So i got five more. It,s driving me up

. I,am not giving up till i or we figure this one out.
Thanks &THANKS Capbuster.

julie_m · 23rd Apr 2010, 11:13 am

If I read that right, the portable set started up again when the Philco stopped. And that means the local oscillator in the Philco (which the portable set was picking up) must have stopped. So now we know where the problem lies.

Have you got a circuit diagram? Pay attention to the local oscillator (which is probably the triode half of a triode-hexode valve). Do not forget the wavechange switch: this forms part of the oscillator circuit, and any poor contact here due to dirt or loss of springiness can prevent oscillation.

Herald1360 · 23rd Apr 2010, 3:41 pm

A 27 valve (tube) is a single triode- a possible choice for a local oscillator, though the data sheet says Detector / Amplifier.

Advice is still relevant, though.....

What is the valve line-up, does anyone know what does which? Newlite?

G8HQP Dave · 23rd Apr 2010, 4:39 pm

According to this website the LO is a 27, feeding a 24 mixer. Its unusual for an oscillator to fail in the middle of the range, usually its at one end.

If it only fails when the set warms up then this suggest not a mechanical problem with the tuning capacitor, but something dropping the gain of the LO (which must be marginal at other frequenices too). Leaky HT decoupler? Resistor changing value? As the OP has tried a number of 27 valves it is unlikely to be a valve problem.

OErjan_S · 23rd Apr 2010, 6:09 pm

uhm, oops, missed that it dropped out after a while.
things like this can actually come from bad solder joint or otherwise loose wire...

capbuster · 23rd Apr 2010, 11:41 pm

Line up of valves are a 80 rect. TWO 45,S PUSH PULL OR 2ND A. F. A 27 OSC.
A27 DECT. AMP 27 - DECT. RECT. - 27 - 1ST -A.F. AND 24 VALVES ARE FIRST
R.F. AND FIRST DECT. AND FIRST I.F. AND SND I.F. . IF THIS HELPS ANY.
Thanks Capbuster.

capbuster · 23rd Apr 2010, 11:45 pm

Dave when you say leaky ht decoupler what are you talking about .
Thanks CAPBUSTER.

Herald1360 · 24th Apr 2010, 12:14 am

Looking at the circuit in the reference Dave gave, the capacitor labelled 49 looks like the HT decoupler for the anode supply to the 27 LO (and also the screen supplies for all the 24 tetrodes).

The circuit is certainly interesting, particularly the method of using the speaker field current to derive the screen supply voltage and also two separate grid bias voltages!

G8HQP Dave · 24th Apr 2010, 9:16 pm

Quote:

Originally Posted by capbuster

Dave when you say leaky ht decoupler what are you talking about .
Thanks CAPBUSTER.

An HT decoupler is a capacitor which reduces unwanted interactions between stages, and may also reduce hum from the power supply. One end of the cap will connect to the chassis, the other end via a resistor to the HT rail. Do Americans call the HT the B supply? I'm not sure. If this capacitor is an old electrolytic or a paper/foil with moisture inside (quite common in old sets) then as it warms up it might conduct DC current instead of blocking it. This will reduce the HT supply to the oscillator and reduce the gain of the valve.

capbuster · 24th Apr 2010, 11:52 pm

Yes we call B . Thanks for responding . Idid replace all the caps even the electrolytic caps or filter caps . But when i ordered the caps it calls for 2uf @450 volts but the company sent 4.7uf instead . would this cause a problem .
This set has a condenser box had 10 caps in it . one hard set to work on.
But it a nice one looks as good as pics on site you found.
Thanks CAPBUSTER

PJL · 25th Apr 2010, 9:12 am

Can you explain symptoms. When you say it stops between 800-1200 does this mean that when rotating the dial it works below 800 and above 1200?

capbuster · 25th Apr 2010, 3:52 pm

When turning dial from 800 , 900, 1000, to 1200. all quiet. Just wondering if
the IF transformer might be cutting out after it warms up. How would i check IF?
Thanks Capbuster.

PJL · 25th Apr 2010, 4:39 pm

Does it work below 800 and above 1200?

22nd Apr 2010, 3:04 pm	#1
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	No reception between 800 and 1200 KHz. Hello . My set plays but after about 25 minutes quits receving from around 800 to 1200 on the dial. No for sure all resisters are good all caps are new tubes just purchased them. And antenna coils check out. Seem like something getting hot cutting out . Does it quick not gradual . Philco model 111 Iknow i brought this up before but can not figure this out. Thanks Denver.

22nd Apr 2010, 3:54 pm	#3
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: 800to 1200 if this was me I would check the tuning capacitor, there might be something shorting it, dust, a stray bead of solder/wire or even a bent vane.

22nd Apr 2010, 4:02 pm	#4
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: 800to 1200 The oscillator is running . I watched all the valves while running. I cleaned the tuning condenser good . Could it be one of the mica caps ? If so which one would it be ?Most reading i done said leave these alone.

22nd Apr 2010, 4:39 pm	#5
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	Re: 800to 1200 This appears to be a very complex set with 11 valves, it is also 80 years old. Faultfinding is likely to be difficult. Try putting the original RF amp and oscillator valves back in and see if that improves things. New old stock valves can come with faults so it is worth checking this. Neil __________________ preserving the recent past, for the distant future.

22nd Apr 2010, 4:57 pm	#6
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: 800to 1200 You won't be able to tell whether the oscillator has stopped just by looking at the valves. Instead, use this method: Get a known-working radio (we'll call this "set 2" and the unknown "set 1"; it's easiest if set 2 is a battery portable). Tune set 2 to a weak station near the top (many kHz, few metres) end of the MW band and place near to set 1, as close as possible to the frequency changer valve. Tune set 1 slowly up the MW band. At some point, set 2 will go quiet as the LO in set 1 (which is equal to the tuned frequency plus the IF; the IF usually being about 470kHz) swamps the signal. If the oscillator in set 1 stops, set 2 will burst back into life again. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

22nd Apr 2010, 3:42 pm	#2
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: 800to 1200 Is the local oscillator running when the set goes quiet? __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

22nd Apr 2010, 5:47 pm	#7
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: No reception between 800 and 1200 KHz. I will try this . Let you know tomorrow have to get to work now . Thanks and thanks Capbuster.

23rd Apr 2010, 1:24 am	#8
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: No reception between 800 and 1200 KHz. Ok that is one neat ideal. It worked good the portable set would quit when tuned to same . But soon as it got warmed up good it quit oscillating . I have ten #27 valves . Tried all of them in set surely all are not bad. What else would cause the set to quit oscillating. PUZZLED. Reason i have ten #27 valves maybe first five were bad. So i got five more. It,s driving me up . I,am not giving up till i or we figure this one out. Thanks &THANKS Capbuster.

23rd Apr 2010, 11:13 am	#9
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: No reception between 800 and 1200 KHz. If I read that right, the portable set started up again when the Philco stopped. And that means the local oscillator in the Philco (which the portable set was picking up) must have stopped. So now we know where the problem lies. Have you got a circuit diagram? Pay attention to the local oscillator (which is probably the triode half of a triode-hexode valve). Do not forget the wavechange switch: this forms part of the oscillator circuit, and any poor contact here due to dirt or loss of springiness can prevent oscillation. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

23rd Apr 2010, 3:41 pm	#10
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: No reception between 800 and 1200 KHz. A 27 valve (tube) is a single triode- a possible choice for a local oscillator, though the data sheet says Detector / Amplifier. Advice is still relevant, though..... What is the valve line-up, does anyone know what does which? Newlite? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

23rd Apr 2010, 4:39 pm	#11
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: No reception between 800 and 1200 KHz. According to this website the LO is a 27, feeding a 24 mixer. Its unusual for an oscillator to fail in the middle of the range, usually its at one end. If it only fails when the set warms up then this suggest not a mechanical problem with the tuning capacitor, but something dropping the gain of the LO (which must be marginal at other frequenices too). Leaky HT decoupler? Resistor changing value? As the OP has tried a number of 27 valves it is unlikely to be a valve problem.

23rd Apr 2010, 6:09 pm	#12
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: No reception between 800 and 1200 KHz. uhm, oops, missed that it dropped out after a while. things like this can actually come from bad solder joint or otherwise loose wire...

23rd Apr 2010, 11:41 pm	#13
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: No reception between 800 and 1200 KHz. Line up of valves are a 80 rect. TWO 45,S PUSH PULL OR 2ND A. F. A 27 OSC. A27 DECT. AMP 27 - DECT. RECT. - 27 - 1ST -A.F. AND 24 VALVES ARE FIRST R.F. AND FIRST DECT. AND FIRST I.F. AND SND I.F. . IF THIS HELPS ANY. Thanks Capbuster.

23rd Apr 2010, 11:45 pm	#14
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: No reception between 800 and 1200 KHz. Dave when you say leaky ht decoupler what are you talking about . Thanks CAPBUSTER.

24th Apr 2010, 12:14 am	#15
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: No reception between 800 and 1200 KHz. Looking at the circuit in the reference Dave gave, the capacitor labelled 49 looks like the HT decoupler for the anode supply to the 27 LO (and also the screen supplies for all the 24 tetrodes). The circuit is certainly interesting, particularly the method of using the speaker field current to derive the screen supply voltage and also two separate grid bias voltages! __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

24th Apr 2010, 11:52 pm	#17
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: No reception between 800 and 1200 KHz. Yes we call B . Thanks for responding . Idid replace all the caps even the electrolytic caps or filter caps . But when i ordered the caps it calls for 2uf @450 volts but the company sent 4.7uf instead . would this cause a problem . This set has a condenser box had 10 caps in it . one hard set to work on. But it a nice one looks as good as pics on site you found. Thanks CAPBUSTER

25th Apr 2010, 9:12 am	#18
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: No reception between 800 and 1200 KHz. Can you explain symptoms. When you say it stops between 800-1200 does this mean that when rotating the dial it works below 800 and above 1200?

25th Apr 2010, 3:52 pm	#19
capbuster Retired Dormant Member Join Date: Mar 2010 Location: Bristol, Virginia, USA. Posts: 31	Re: No reception between 800 and 1200 KHz. When turning dial from 800 , 900, 1000, to 1200. all quiet. Just wondering if the IF transformer might be cutting out after it warms up. How would i check IF? Thanks Capbuster.

25th Apr 2010, 4:39 pm	#20
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	Re: No reception between 800 and 1200 KHz. Does it work below 800 and above 1200?