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TonyDuell · 7th Aug 2018, 2:49 pm

Like many Bush sets of the period, the really high frequency stuff is in a metal box on top of the chassis. There are 2 (square) coil cans on it, with a valve between them.

Do not even move any components inside this unit until you know what you are doing. In fact don't open it at this stage. The reason is that the wires of the various components form small capacitors with each other. And the sort of frequencies involved these 'capacitors' matter. Move the components and you change their values and you might have to re-align the set (not something to do until you get a bit more experience).

A few more 'Don'ts' for the benefit of the set and for you.

Don't twiddle any of the coil cores or trimmer capacitors. It is unlikely any fault is caused by these being incorrectly set (unless somebody has been there before you). But if they are mis-adjusted then even with everything else being right you will get no or poor reception. Adjusting them properly ('alignment') generally needs at least a good signal generator

Don't, whatever you do, work with one hand resting on the metal chassis and the other probing around. If you accidentally touch a high voltage point with said free hand the current will flow across your body via your heart. The result can be fatal. As Kalee20 said, work with one hand (and keep your other hand behind your back or firmly in your pocket).

If possible never work alone. Have somebody else around who can keep half an eye on you and who knows how to turn off the power if anything goes seriously wrong. Try to ensure they know the difference between 'ouch' and 'I'm unconcious'...

I'll agree that a lamp limiter is a very useful thing to have. Having done various temporary bodges in the past, I made a 'proper' one earlier this year. I now use it all the time.

With this sort of set I'd start by replacing the capacitor known here as 'that capacitor'. It's C65 on the Trader Sheet circuit. After doing that, switch on with a lamp limiter in the mains supply and assuming the lamp doesn't glow brightly (indicating a short circuit somewhere), check the HT+ voltage and the electrode voltages of the EL84, comparing them against the service information. If that all seems OK, select 'Gram' and feed an audio signal (even just touching the socket to input a bit of mains hum) into the 'PU' (pickup) sockets and thus see if the audio stages are working.

7th Aug 2018, 2:49 pm	#8
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Bush VHF61 restoration Like many Bush sets of the period, the really high frequency stuff is in a metal box on top of the chassis. There are 2 (square) coil cans on it, with a valve between them. Do not even move any components inside this unit until you know what you are doing. In fact don't open it at this stage. The reason is that the wires of the various components form small capacitors with each other. And the sort of frequencies involved these 'capacitors' matter. Move the components and you change their values and you might have to re-align the set (not something to do until you get a bit more experience). A few more 'Don'ts' for the benefit of the set and for you. Don't twiddle any of the coil cores or trimmer capacitors. It is unlikely any fault is caused by these being incorrectly set (unless somebody has been there before you). But if they are mis-adjusted then even with everything else being right you will get no or poor reception. Adjusting them properly ('alignment') generally needs at least a good signal generator Don't, whatever you do, work with one hand resting on the metal chassis and the other probing around. If you accidentally touch a high voltage point with said free hand the current will flow across your body via your heart. The result can be fatal. As Kalee20 said, work with one hand (and keep your other hand behind your back or firmly in your pocket). If possible never work alone. Have somebody else around who can keep half an eye on you and who knows how to turn off the power if anything goes seriously wrong. Try to ensure they know the difference between 'ouch' and 'I'm unconcious'... I'll agree that a lamp limiter is a very useful thing to have. Having done various temporary bodges in the past, I made a 'proper' one earlier this year. I now use it all the time. With this sort of set I'd start by replacing the capacitor known here as 'that capacitor'. It's C65 on the Trader Sheet circuit. After doing that, switch on with a lamp limiter in the mains supply and assuming the lamp doesn't glow brightly (indicating a short circuit somewhere), check the HT+ voltage and the electrode voltages of the EL84, comparing them against the service information. If that all seems OK, select 'Gram' and feed an audio signal (even just touching the socket to input a bit of mains hum) into the 'PU' (pickup) sockets and thus see if the audio stages are working.