Bush VHF64 - ECC85 gobbler? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

Steve_P · 16th Sep 2009, 1:56 pm

There are some caps on the heater chain in the VHF can. C2, C11 and C12 on the trader sheet. Also C25.

Clutching at straws I know, but it's all I can think of if nothing's getting hot. (Apart from things that should, I mean.)

Cheers,

Steve P.

jjl · 16th Sep 2009, 2:07 pm

Brian

I think your low heater supply voltage is due to either of the following

1. A high resistance path in series with the heater supply.
2. Some component drawing excessive current from the heater supply.
3. A transformer fault.

For 1, check all soldered joints in the heater supply at valve bases, dial lamps, the transformer itself and any soldered or screw connection to the chassis.

For 2, suspect any decoupling components in the heater supply, I'm not sure whether the VHF64 has any, they may be in the FM tuner box.

For 3, disconnect one end of the heater supply at the transformer and measure the off-load heater supply voltage, if this is still low your transformer probably has shorted turns.

Hope this helps.

John

monoman · 16th Sep 2009, 2:07 pm

I don't feel confident or competent enough to remove and open up the FM module Steve. When I look in the manual photocopy it looks like a no-go area for such timorous souls as I

Brian.

Hunts smoothing bomb · 16th Sep 2009, 2:17 pm

Quote:

Originally Posted by jjl

1. A high resistance path in series with the heater supply.
John

Hmm, I would have thought that if the fault was a high resistance path then removing a dial lamp should produce a notable raise in voltage? so I guess it's not that. I wonder if it could be the tranny?

Cheers

monoman · 16th Sep 2009, 2:34 pm

Maybe I'll have to try and squeeze in a 6.3V 4A transformer somewhere.

Somehow I missed your last post John. There are a couple of small caps on LT+ other than in the FM box, one at the ECH81 base and one at the second EF89 base. I'll check those out first.

Brian.

geofy · 16th Sep 2009, 2:50 pm

Quote:

Originally Posted by monoman

Geof, are you still living in Ongar?

Brian.

Nearby Shelley actually, briefly going OT

Geof

monoman · 16th Sep 2009, 2:52 pm

I'll PM you.

Quote:

Originally Posted by geofy

Quote:

Originally Posted by monoman

Geof, are you still living in Ongar?

Brian.

Nearby Shelley actually, briefly going OT

Geof

julie_m · 16th Sep 2009, 3:01 pm

Pull out the valves one at a time, while a meter is connected across the heater line, and see which one makes the most difference.

Ordinarily the EZ and EL will be the hungriest. You've got to put more heat into a cathode to get more electrons to come out of it. All the current for the set is flowing through the rectifier; and the lion's share of that ends up flowing through the speaker transformer, and hence the output pentode.

jjl · 16th Sep 2009, 3:02 pm

Brian

A bit of a long shot but..

The 6P14P is supposed to be an EL84 equivalent with the same 760mA heater current, but it's just possible that your 6P14 is marked as such but is in fact a similar valve with different heater current requirements. This sort of thing does happen with modern valves from Russia, China and the like.

Anyway, I suggest that you remove the 6P14 and then measure the heater voltage.

John

monoman · 16th Sep 2009, 3:27 pm

OK. All valves and one pilot light removed I get 7.1V. Replacing the EZ81 this drops to 5.8V whichever of the two to hand I use and when I replace the 6P14-EV I get 5.6V.

Brian.

monoman · 16th Sep 2009, 4:19 pm

My hope is that it is one of the heater decoupling caps - but not one in The Box!

Brian.

Nickthedentist · 16th Sep 2009, 4:24 pm

Don't be scared of The Box, it's not that bad

jjl · 16th Sep 2009, 4:26 pm

Brian

OK, that sounds like you have resistance in series with the heaters that shouldn't be present. This must be either in the heater wiring or in a solder joint or chassis joint.

Is the EZ81 electrically closest to the heater winding of the transformer i.e. is it the first valve in the heater chain?

John

paulsherwin · 16th Sep 2009, 4:35 pm

It does sound as if there is some resistance in the heater circuit somewhere, maybe a dry joint on the transformer connections.

Running an ECC85 with 5.3V on the heater is likely to lead to a short service life (and poor performance too).

Measure the AC voltage between the first valve in the heater wiring and the transformer. You should find maybe 1V AC voltage drop. Once this has been established you just need to find out what's causing it.

Fitting an additional heater transformer is an overreaction at this stage. There's more fault finding to be done first.

Paul

monoman · 16th Sep 2009, 4:35 pm

Quote:

Originally Posted by jjl

Is the EZ81 electrically closest to the heater winding of the transformer i.e. is it the first valve in the heater chain?

It is indeed John.

Brian.

monoman · 16th Sep 2009, 4:50 pm

I measure 5.8V at the transformer terminal with just the EZ81 (and one pilot light) in circuit, 6.9V with it out so the loss seems to be occurring within the transformer. With no valves and no pilot light bulbs I measure just over 2 ohms from the 6.3V terminal to chassis. The service manual says "L.T.Sec. less than 0.5".

Brian.

Lee de Forest · 16th Sep 2009, 5:07 pm

I had a faulty ECC85 in my Blaupunct Sultan. FM started O.K. and then used to fade in and out. Visual inspection showed what looked to be distortion of the plates and discolouration due to heat. Heater voltage measured 6.3v. I replaced the valve with a second hand one of unknown origin and it has been working fine over the last year with approx. 1 hours use a week.
Take the bulbs out and measure the heater voltage to see what happens.

Steve_P · 16th Sep 2009, 5:27 pm

I was told by an Ex-Engineer that Ferranti/Ekco stuff tended to be suspect about that time. Capacitor change mods, etc.

I think the Ferranti valves (and GEC) were made by Osram.

All hearsay, but you never know.

Is it the heaters that fail by the way?

Cheers,

Steve P.

jjl · 16th Sep 2009, 5:49 pm

Brian

I think we're getting close, and as Paul stated, underrunning the heater of an ECC85 is very likely to shorten its life.

Is the chassis used as a return for the heater supply or are there a pair of wires to the heater connections to each valve?

Does the transformer have tags or flying leads for the heater winding? Can you measure the resistance directly across the heater winding with all valves and lamps removed? If the resistance directly across the winding is high then you have a poor joint between the transformer winding and tags / leads or possibly corrosion in the winding.

John

monoman · 16th Sep 2009, 5:55 pm

Closure! It was a poor interface between the earthing tag and chassis

Ah well, a trip around the houses is always educational

A big thank you to all who have proffered suggestions, your readiness to help is very much appreciated by this radio newbie

Phew! I'm exhausted. Refreshment is called for. My round I think gents

Brian.

16th Sep 2009, 1:56 pm	#21
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF64 - ECC85 gobbler? There are some caps on the heater chain in the VHF can. C2, C11 and C12 on the trader sheet. Also C25. Clutching at straws I know, but it's all I can think of if nothing's getting hot. (Apart from things that should, I mean.) Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

16th Sep 2009, 2:07 pm	#22
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Bush VHF64 - ECC85 gobbler? Brian I think your low heater supply voltage is due to either of the following 1. A high resistance path in series with the heater supply. 2. Some component drawing excessive current from the heater supply. 3. A transformer fault. For 1, check all soldered joints in the heater supply at valve bases, dial lamps, the transformer itself and any soldered or screw connection to the chassis. For 2, suspect any decoupling components in the heater supply, I'm not sure whether the VHF64 has any, they may be in the FM tuner box. For 3, disconnect one end of the heater supply at the transformer and measure the off-load heater supply voltage, if this is still low your transformer probably has shorted turns. Hope this helps. John

16th Sep 2009, 2:07 pm	#23
monoman Retired Dormant Member Join Date: Jan 2008 Location: Ongar, Essex, UK. Posts: 74	Re: Bush VHF64 - ECC85 gobbler? I don't feel confident or competent enough to remove and open up the FM module Steve. When I look in the manual photocopy it looks like a no-go area for such timorous souls as I Brian.

16th Sep 2009, 2:34 pm	#25
monoman Retired Dormant Member Join Date: Jan 2008 Location: Ongar, Essex, UK. Posts: 74	Re: Bush VHF64 - ECC85 gobbler? Maybe I'll have to try and squeeze in a 6.3V 4A transformer somewhere. Somehow I missed your last post John. There are a couple of small caps on LT+ other than in the FM box, one at the ECH81 base and one at the second EF89 base. I'll check those out first. Brian. Last edited by monoman; 16th Sep 2009 at 2:51 pm.

16th Sep 2009, 3:01 pm	#28
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Bush VHF64 - ECC85 gobbler? Pull out the valves one at a time, while a meter is connected across the heater line, and see which one makes the most difference. Ordinarily the EZ and EL will be the hungriest. You've got to put more heat into a cathode to get more electrons to come out of it. All the current for the set is flowing through the rectifier; and the lion's share of that ends up flowing through the speaker transformer, and hence the output pentode. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

16th Sep 2009, 3:02 pm	#29
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Bush VHF64 - ECC85 gobbler? Brian A bit of a long shot but.. The 6P14P is supposed to be an EL84 equivalent with the same 760mA heater current, but it's just possible that your 6P14 is marked as such but is in fact a similar valve with different heater current requirements. This sort of thing does happen with modern valves from Russia, China and the like. Anyway, I suggest that you remove the 6P14 and then measure the heater voltage. John

16th Sep 2009, 3:27 pm	#30
monoman Retired Dormant Member Join Date: Jan 2008 Location: Ongar, Essex, UK. Posts: 74	Re: Bush VHF64 - ECC85 gobbler? OK. All valves and one pilot light removed I get 7.1V. Replacing the EZ81 this drops to 5.8V whichever of the two to hand I use and when I replace the 6P14-EV I get 5.6V. Brian.

16th Sep 2009, 4:19 pm	#31
monoman Retired Dormant Member Join Date: Jan 2008 Location: Ongar, Essex, UK. Posts: 74	Re: Bush VHF64 - ECC85 gobbler? My hope is that it is one of the heater decoupling caps - but not one in The Box! Brian.

16th Sep 2009, 4:24 pm	#32
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,861	Re: Bush VHF64 - ECC85 gobbler? Don't be scared of The Box, it's not that bad

16th Sep 2009, 4:26 pm	#33
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Bush VHF64 - ECC85 gobbler? Brian OK, that sounds like you have resistance in series with the heaters that shouldn't be present. This must be either in the heater wiring or in a solder joint or chassis joint. Is the EZ81 electrically closest to the heater winding of the transformer i.e. is it the first valve in the heater chain? John

16th Sep 2009, 4:35 pm	#34
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,965	Re: Bush VHF64 - ECC85 gobbler? It does sound as if there is some resistance in the heater circuit somewhere, maybe a dry joint on the transformer connections. Running an ECC85 with 5.3V on the heater is likely to lead to a short service life (and poor performance too). Measure the AC voltage between the first valve in the heater wiring and the transformer. You should find maybe 1V AC voltage drop. Once this has been established you just need to find out what's causing it. Fitting an additional heater transformer is an overreaction at this stage. There's more fault finding to be done first. Paul

16th Sep 2009, 4:50 pm	#36
monoman Retired Dormant Member Join Date: Jan 2008 Location: Ongar, Essex, UK. Posts: 74	Re: Bush VHF64 - ECC85 gobbler? I measure 5.8V at the transformer terminal with just the EZ81 (and one pilot light) in circuit, 6.9V with it out so the loss seems to be occurring within the transformer. With no valves and no pilot light bulbs I measure just over 2 ohms from the 6.3V terminal to chassis. The service manual says "L.T.Sec. less than 0.5". Brian. Last edited by monoman; 16th Sep 2009 at 5:08 pm.

16th Sep 2009, 5:07 pm	#37
Lee de Forest Retired Dormant Member Join Date: Sep 2008 Location: Harrogate, North Yorkshire, UK. Posts: 352	Re: Bush VHF64 - ECC85 gobbler? I had a faulty ECC85 in my Blaupunct Sultan. FM started O.K. and then used to fade in and out. Visual inspection showed what looked to be distortion of the plates and discolouration due to heat. Heater voltage measured 6.3v. I replaced the valve with a second hand one of unknown origin and it has been working fine over the last year with approx. 1 hours use a week. Take the bulbs out and measure the heater voltage to see what happens.

16th Sep 2009, 5:27 pm	#38
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF64 - ECC85 gobbler? I was told by an Ex-Engineer that Ferranti/Ekco stuff tended to be suspect about that time. Capacitor change mods, etc. I think the Ferranti valves (and GEC) were made by Osram. All hearsay, but you never know. Is it the heaters that fail by the way? Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

16th Sep 2009, 5:49 pm	#39
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Bush VHF64 - ECC85 gobbler? Brian I think we're getting close, and as Paul stated, underrunning the heater of an ECC85 is very likely to shorten its life. Is the chassis used as a return for the heater supply or are there a pair of wires to the heater connections to each valve? Does the transformer have tags or flying leads for the heater winding? Can you measure the resistance directly across the heater winding with all valves and lamps removed? If the resistance directly across the winding is high then you have a poor joint between the transformer winding and tags / leads or possibly corrosion in the winding. John

16th Sep 2009, 5:55 pm	#40
monoman Retired Dormant Member Join Date: Jan 2008 Location: Ongar, Essex, UK. Posts: 74	Re: Bush VHF64 - ECC85 gobbler? Closure! It was a poor interface between the earthing tag and chassis Ah well, a trip around the houses is always educational A big thank you to all who have proffered suggestions, your readiness to help is very much appreciated by this radio newbie Phew! I'm exhausted. Refreshment is called for. My round I think gents Brian.