Bush VHF64 - Help required please!

[ekjdm14]

Have you looked at the small electrolytic mentioned above yet, or tried swapping the EABC80?

I had a regular light "pop" on a VHF61, (was simultaneously getting very low VHF reception although not dead, magic eye was showing strong signal even between stations on all bands) IIRC it was a damaged replacement cap that I'd not noticed, may have been in the AGC circuit but memory eludes me as to exactly which and where.

[crackle]

Look out for small capacitors which look similar to resistors with bullet shaped ends, 1000pf (brown black red) was a very common value, these can be as leaky as the brown Hunts caps.

Mike

[Gavman68]

Originally Posted by ekjdm14

Have you looked at the small electrolytic mentioned above yet, or tried swapping the EABC80?

I had a regular light "pop" on a VHF61, (was simultaneously getting very low VHF reception although not dead, magic eye was showing strong signal even between stations on all bands) IIRC it was a damaged replacement cap that I'd not noticed, may have been in the AGC circuit but memory eludes me as to exactly which and where.

Originally Posted by crackle

Look out for small capacitors which look similar to resistors with bullet shaped ends, 1000pf (brown black red) was a very common value, these can be as leaky as the brown Hunts caps.

Mike

Thanks chaps. I have replaced the cap mentioned but will take a fresh look at those other caps and replace those as well. VHF doesn't even move the magic eye across the whole range so it seems dead. I have spare valves from the donor chassis so will try swapping those out one by one and check all the solder points on the underside of the valve pins to see if any look particularly suspect. The only thing I haven't changed so far is the main smoothing cap can which considering is dated Nov 1957 probably could do with replacing. Trying to source some reasonable value 40uf 350Vdc+ caps is proving difficult however. At least I'm making progress, it sounds great on the 4-5 channels I can get on MW (bar the intermittent popping sound) but I am keen to get the VHF working too.

In other news I just picked up a Bush VHF61 in superb unblemished condition for just £10! That will be the next project and also what to do with the other VHF64 donor chassis and cabinet?

[Gavman68]

Swapped out each valve in turn and I think the popping/screeching noise issue was a dodgy EL84 valve. The pristine looking Pinnacle EL84 was replaced with a worn and blackened Mullard and the noise issue went away.

[Sideband]

Originally Posted by Sideband

Without getting too technical at this stage, try cleaning the wavechange switch with Servisol. There will be a pair of contacts switching the HT to the FM tuner and these may have corroded over the years. If this doesn't help, you will have to look at the circuit and find the said contacts and check with a meter that they are actually switching OK. I think it highly unlikely that you will have two faulty FM tuners, so something very basic and fundamental is more likely....like no HT being switched to the tuner.

Have you established that there is in fact HT getting to the tuner? No point in doing anything else until you have.

[yestertech]

Once you've established that there's HT getting to the ECC85 ( easiest to measure at the valve pins ) then you may have a 'dead' IF section. Whilst the IFT windings just be intact ( as MW/LW is working ) they could be seriously misaligned to the point where there's no IF output at all - maybe even a broken/missing slug. Can you inject 10.7 mHz into the IF strip to check ??


Andy

[Gavman68]

After much tinkering and fettling I have somehow managed to get a perfect FM response from this set. The thing is I'm not exactly sure how I managed it? I swapped out various valves with the other donor set, changed a few more resistors and double checked all the Hunts caps were all replaced (they were) and checked as many soldered joints as I could to see if any were suspect. Now with a cheap FM antenna plugged into the aerial connections I get great FM coverage all across the band. MW is still ok and I imagine would be better with a decent aerial attached but for now the set has been bench tested over the last few weeks and sounds great. I still have a light intermittent pop/ticking sound on FM particularly when warmed up after an hour or more so I guess my tinkering is not complete but I'm getting closer to having a really good set. Magic eye is bright as you like and opens and closes well in tune with the sound signal. The other donor set I converted into a bluetooth speaker and having repaired the cracked and torn speakers with several light PVA coatings (which worked really well!) it also now sounds great. I picked up a bakelite VHF61 for a tenner recently and with my experience gained restoring the VHF64 it was a quick restorations and that too now operates well. I think I've caught the restoration/renovation bug now!!