Bush VHF64 - Help required please!

[Gavman68]

Hello All!

I'm in the process of refurbishing a VHF64 S/N 220/2019, so it looks like an earlier model. I'm about to start re-capping the entire set and have noticed a few anomalies with this set that I'm hoping some of you may be able to shed some light on and assist me!?

First, the set has no magic eye set up, the entire unit is missing along with any associated circuitry, the window where the magic eye shines through has even had black paint applied on the inside, and this has been deliberately done. From heat marks behind where the valve would have sat it obviously was there at some stage but looks very much like it was done early in its lifespan, perhaps the owner had a valve failure and couldn't be bothered or afford to repair it correctly so had it removed, has anyone else come across a missing magic eye before and will it affect the operation of the set once working?

Second, I have been poring over the circuit diagram working out what capacitors I need etc. and unless I'm reading it wrong, I seem to have a resistor in place where a capacitor should be. Hopefully, the photos attached explain, but it seems according to the circuit diagram, C55 should be in place where indicated however from the picture of my chassis it looks like a resistor is in its place? Could this have something to do with the magic eye removal perhaps? I am very much a novice in this field and so don't fully understand some of the terminologies I've seen used in similar threads so would appreciate being replied to like I'm an idiot!

And finally, can I replace the four wax-covered flat capacitors indicated by blue arrows?

Any help greatly appreciated.

[stevehertz]

That "resistor" is C55, a capacitor. Capacitors also used colour codes: https://www.electronics-tutorials.ws...tor/cap_5.html

[Gavman68]

Cheers Steve, I had literally just stumbled across that section and realised it was in fact a type of resistor, problem solved then

[Herald1360]

C55 is a ceramic capacitor and is unlikely to need replacing.

The flat waxy capacitors C16, C23-25 are silver mica and also unlikely to be faulty.

The only paper dielectric capacitors which are reasonable to leave alone are ones in low impedance circuitry (less than about 10k) like RF /IF cathode bypass where their leakiness is unlikely to upset dc conditions. Obviously if they've gone short or low capacitance even these should be replaced.

[stitch1]

Originally Posted by Gavman68

I'm in the process of refurbishing a VHF64 S/N 220/2019, so it looks like an earlier model. I'm about to start re-capping the entire set

I assume you're not literally going to re-cap the whole set?

Personally I'd only change the audio coupling cap, do some safety checks and power it up to see if it works at all. No point changing caps to find out there’s a major fault somewhere.

if you need to change any caps it will just be the larger paper ones and brown hunts not the small value ones. changing the small value ones especially in the tuner section will cause all sorts of problems.


John

[Gavman68]

Cheers John,

When I say entire set I meant all the Hunts and Paper wax caps, I think as you say an entire re-cap would be unnecessary and also take forever!

[Tractionist]

Yep - change the waxies, and the hunts .... generally the decouplers - you'll have to do approximately thirty-two from recollection. (leave the rf / silver / wax plated stuff alone if you can.)

[Sideband]

With regards to the magic eye/tuning indicator, it's removal will in no way affect the performance of the radio. It might have been removed as a cost-cutting exersise....I have seen that before with other manufacturers. I think if someone had just removed the eye because it didn't work, it's highly unlikely they would have removed the rest of the circuitry (or even known how to). More than likely a decision was made by the manufacturer (possibly due to availability problems and manufacturing deadlines) to produce sets without the magic eye and so blanked the window and left the rest of the circuitry out. Later sets probably had the eye fitted.

[stevehertz]

I agree. I just wonder how a retailer was supposed to overcome that shortcoming to a prospective buyer when the published spec and user manual would clearly state that the set had a magic eye - a great feature back then. Not to mention the glaring 'hole' in the set where it once was. Ok, I get that many buyers would not even notice, but that's selling an item at full price but not fully featured as specified. Perhaps they were told by Bush reps to point out the omission and offer a reduction. No-one knows, but an interesting situation.

[Gavman68]

Originally Posted by Gavman68

Cheers Steve, I had literally just stumbled across that section and realised it was, in fact, a type of resistor, problem solved then

I meant a capacitor! So far I've worked out which capacitors will require changing and tested most of the resistors. Most resistors were OK, but a few out of spec beyond the generous tolerance values so they'll be getting changed too.

Thanks for your comments so far, they've been helpful.

[Sideband]

Don't be too critical of resistors....seriously....some can drift by as much as 30 or 40 percent and the set will still perform OK. Of course it depends on where the resistor(s) are in the circuit and a certain amount of experience is required to know where you can get away with it. No harm in changing them if you want to of course.

[stevehertz]

Well there's the rub, knowing the circuit positions where out of tolerance resistors are not problematic. Having restored a set, if it's still not 100% I'll sometimes resort to checking resistor values, and my own rule of thumb for a 'pass' is 20% tolerance.

[Gavman68]

So I've re-capped the set and replaced a number of resistors. Getting good reception on MW on about 3 stations but nothing on SW, barely anything on LW and nothing at all on FM, not sure where to start to fix the FM and ideally id like this band to work the most, any tips?

[cathoderay57]

Presumably you are only using the ferrite rod aerial and if so you wouldn't expect to get signals on the SW band. If you plug a length of wire into the AM aerial socket you should get better reception. The FM performance on sets of this era typically suffer from low emission ECC85 valves. Unless you can get yours tested then it would be worth trying a replacement. Cheers, Jerry

[David G4EBT]

I'd concur with Jerry's comments. ECC85s are in my experience generally the culprit for no FM. I do wonder if that's why many AM/FM sets were 'pensioned off'. It's reasonable to assume that they were mostly used on FM and when the set failed, the cost of taking it to a dealer, paying for the diagnosis and a new valve would have deterred users from spending money on the set. By the early 1960s, TV viewing was in the ascendancy and radio listening was in decline.

As to reception, the instructions make it clear that for SW reception and external aerial is needed. On FM, the internal 'aerial' - such that it is - is stated as for the reception of 'local' stations. With a good ECC85, the set might work well enough on FM, but it would work much better with an external FM aerial - even one of those cheap ribbon jobbies draped around.

https://www.ebay.co.uk/itm/Indoor-FM...sAAOSwkNReDK8i

If the EM81 magic eye is good, when stations are tuned in, you may not see much of a change except on strong signals, especially without an external aerial as the eye depends on a swing of several volts on the AVC line for the display to alter much.

A lovely set by the way and it looks in good shape too - expensive in its day - £35.10s in 1957 + Purchase tax, say £50 in all.
That equates to about £1,200 today when adjusted for inflation. No wonder they were put in the loft and not thrown away!

Every success with it.

[Gavman68]

Thanks for all the tips chaps, I'm getting nothing on FM with an aerial connected, not even the faintest variation in sound just a hum. I swapped the VHF tuning module for another from a second VHF64 I have awaiting restoration and it was exactly the same result. I tried the ECC85 from the other set and then put an unused NOS Siemens ECC85 valve in for good measure but had the same result. I'm stuck now to determine why I have no FM reception.

[stevehertz]

I know this isn't a very technical tip, but try cleaning all the valve bases and switches with Servisol switch cleaner. That will at least eliminate problems in those areas.

[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.

[cathoderay57]

The FM demodulator uses 2 of the 3 diodes of the EABC80. There is a small electrolytic capacitor between one of the diode's anodes and the other's cathode (5uF probably <25v). If you haven't replaced the cap it is worth a try. Be careful though because the positive lead of the cap goes to chassis. If the cap or the 2 diodes of the EABC80 have failed you will get no sigs on FM while AM might work fine. Cheers, Jerry

[Gavman68]

Thanks for the tips so far. Update - I've replaced all the hunts, wax and paper caps and around half a dozen resistors. Also replaced mains wiring, speaker wiring, quite a few of the wires off the main transformer and all 3 to the smoothing cap and all the magic eye wiring. I can now get pretty good MW reception using just the internal aerial but still nothing at all on VHF. Also every 15-20 secs there is a light popping noise regardless if it is tuned to any station. I've cleaned the wave guides as best I can but don't know what to do next? This set is s/n 220/2450 and has the anti hum mod unlike my other set 220/2019 so this mod came in somewhere between this range.