Bush VHF 64 what have I done? - UK Vintage Radio Repair and Restoration Discussion Forum

PWH · 22nd Jun 2009, 11:52 am

OK so the restoration was going well =all Hunts caps replaced, fired up works OK on MW & SW. No hum!

Noticed the EABC 80 valve holder was really dodgy and giving intermittent contact so decided to change it. Drew out where everything went ( I thought) and change the valve holder. Fired up again and it screeches like h*ll.

Pulled the eabc 80 and just a faint hum of life- Checked all the connections and even took them all off and re did them and it still screeches. Tried a different EABC 80. same result. So I have done something wrong!

The 6.8M resistor is connected to the centre of the valve holder as an anchor and I drew it as connecting to pin 7, which is shown as connecting to chassis
I did not note down where this was taken to chassis. I have used pin 5 the heater return point .

Remove this and all the screeching goes but no signal. Any ideas? Could a kind soul who has one take a photo of this area and post it here.

Thanks

Steve_P · 22nd Jun 2009, 3:34 pm

Have you put all the wires back in the same place. It's surprising sometimes.

Try not using the heater pin at all. Take that cap to deck in the middle and not via the pin.

Does it do this on all bands?

Check your wiring against the Bush Manual. It does have a diagram of sorts.

Cheers,

Steve P.

yestertech · 23rd Jun 2009, 8:59 am

Tricky to photo as it's still in the cabinet so I've snapped it through the access hatch in the base.
Hopefully this should assist you in getting everything order back the in right !

Andy

geofy · 23rd Jun 2009, 3:11 pm

I can’t quite make out pin1 of your picture but the 6M8 appears to be connected to pin 8 (triode grid), (has this value changed because of soldering). It ‘sounds’ as if you may have introduced positive feedback, if you have connected the 6M8 to pin7 cathode.

Geof

PWH · 23rd Jun 2009, 6:53 pm

Thank you guys & Setsappeal for the photo. I see what I have done. I'll go and try it and report back...

PWH · 23rd Jun 2009, 7:09 pm

If I could just clarify
The black wire connecting to the tag strip- the end pointing at the green band on the resistor - Is that wire the only connection to that pin?

The resistor- what is the wire at the blue end connected to? From the photo It looks like the yellow & brown wire but I don't think so..

Thanks again Guys..

PWH · 29th Jun 2009, 4:10 pm

The problem was that the black wire shown in the photo had dropped off when I was unsoldering the other end. Not knowing where it came from I guessed (wrong) so the lesson learnt is take a photo first.!

The AM now works marvellously on all bands but FM only produces a faint hiss. Tried various ECC85's and have a new EABC 80 and ECL 81but not a hint of audio.. Any clues how to diagnose??
Thanks
Peter

yestertech · 29th Jun 2009, 4:28 pm

Quote:

Originally Posted by PWH

The problem was that the black wire shown in the photo had dropped off when I was unsoldering the other end. Not knowing where it came from I guessed (wrong) so the lesson learnt is take a photo first.!

Peter

Easily done Peter - Glad it's now 'better' I was going to say working, but clearly there's more to do !

According to the manufacturers data, around 17ma of HT should be drawn by the VHF tuner unit. If you measure across switch S6B with the set on AM, you should be able to check this to see if both halves of the ECC85 are drawing current. Much less and you may have a faulty anode feed resistor ( R2,R4 ) or much more ,a defective decoupler ( C4, C7 ) . Failing that, could anyone have tweaked the IFT adjustments ?
To get top drawer performance, you'll probably have to change both EF89s as these lose emission quite badly.

Andy

Steve_P · 29th Jun 2009, 5:11 pm

First thing to do is see if 10.7 gets out OK. If it does it's the VHF box. If it does not, go forward to the IF stages.

Those pushbuttton wavechange switches are the root of all evil by the way...

Cheers,

Steve P.

PWH · 7th Jul 2009, 8:17 am

Following Setsappeal's advice I noted no current being drawn, thenthat the ECC85 was stone cold. A dodgy valve holder was found to be the culprit and tweaked.. Once the valve got hot, it worked!.

Set now working splendidly

Thanks all.

yestertech · 7th Jul 2009, 11:13 am

Excellent news - These are great sounding radios A.

monoman · 7th Jul 2009, 6:11 pm

Quote:

Originally Posted by setsappeal

Excellent news - These are great sounding radios A.

I heartily concur! Glad you got it sorted Peter.

Brian.

PWH · 7th Jul 2009, 7:38 pm

Out of interest this is in the 4000 serial No range and has the factory humbucking mod

22nd Jun 2009, 11:52 am	#1
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Bush VHF 64 what have I done? OK so the restoration was going well =all Hunts caps replaced, fired up works OK on MW & SW. No hum! Noticed the EABC 80 valve holder was really dodgy and giving intermittent contact so decided to change it. Drew out where everything went ( I thought) and change the valve holder. Fired up again and it screeches like h*ll. Pulled the eabc 80 and just a faint hum of life- Checked all the connections and even took them all off and re did them and it still screeches. Tried a different EABC 80. same result. So I have done something wrong! The 6.8M resistor is connected to the centre of the valve holder as an anchor and I drew it as connecting to pin 7, which is shown as connecting to chassis I did not note down where this was taken to chassis. I have used pin 5 the heater return point . Remove this and all the screeching goes but no signal. Any ideas? Could a kind soul who has one take a photo of this area and post it here. Thanks

22nd Jun 2009, 3:34 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF 64 what have I done? Have you put all the wires back in the same place. It's surprising sometimes. Try not using the heater pin at all. Take that cap to deck in the middle and not via the pin. Does it do this on all bands? Check your wiring against the Bush Manual. It does have a diagram of sorts. 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...?

23rd Jun 2009, 8:59 am	#3
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,130	Re: Bush VHF 64 what have I done? Tricky to photo as it's still in the cabinet so I've snapped it through the access hatch in the base. Hopefully this should assist you in getting everything order back the in right ! Andy Attached Thumbnails

23rd Jun 2009, 3:11 pm	#4
geofy Retired Dormant Member Join Date: Jun 2006 Posts: 1,798	Re: Bush VHF 64 what have I done? I can’t quite make out pin1 of your picture but the 6M8 appears to be connected to pin 8 (triode grid), (has this value changed because of soldering). It ‘sounds’ as if you may have introduced positive feedback, if you have connected the 6M8 to pin7 cathode. Geof Attached Thumbnails

23rd Jun 2009, 6:53 pm	#5
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Bush VHF 64 what have I done? Thank you guys & Setsappeal for the photo. I see what I have done. I'll go and try it and report back...

23rd Jun 2009, 7:09 pm	#6
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Bush VHF 64 what have I done? If I could just clarify The black wire connecting to the tag strip- the end pointing at the green band on the resistor - Is that wire the only connection to that pin? The resistor- what is the wire at the blue end connected to? From the photo It looks like the yellow & brown wire but I don't think so.. Thanks again Guys..

29th Jun 2009, 4:10 pm	#7
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Bush VHF 64 what have I done? The problem was that the black wire shown in the photo had dropped off when I was unsoldering the other end. Not knowing where it came from I guessed (wrong) so the lesson learnt is take a photo first.! The AM now works marvellously on all bands but FM only produces a faint hiss. Tried various ECC85's and have a new EABC 80 and ECL 81but not a hint of audio.. Any clues how to diagnose?? Thanks Peter

29th Jun 2009, 5:11 pm	#9
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Bush VHF 64 what have I done? First thing to do is see if 10.7 gets out OK. If it does it's the VHF box. If it does not, go forward to the IF stages. Those pushbuttton wavechange switches are the root of all evil 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...?

7th Jul 2009, 8:17 am	#10
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Bush VHF 64 what have I done? Following Setsappeal's advice I noted no current being drawn, thenthat the ECC85 was stone cold. A dodgy valve holder was found to be the culprit and tweaked.. Once the valve got hot, it worked!. Set now working splendidly Thanks all.

7th Jul 2009, 11:13 am	#11
yestertech Nonode Join Date: Dec 2002 Location: Coulsdon, Surrey, UK. Posts: 2,130	Re: Bush VHF 64 what have I done? Excellent news - These are great sounding radios A.

7th Jul 2009, 7:38 pm	#13
PWH Heptode Join Date: Mar 2003 Location: Waiheke Island, New Zealand Posts: 503	Re: Bush VHF 64 what have I done? Out of interest this is in the 4000 serial No range and has the factory humbucking mod