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Old 4th Aug 2018, 6:24 pm   #1
sprdsht
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Default Bush VHF61 restoration

Hello, i am 16 and wish to embark on my first foray into the valve world. My knowledge of electronics is fairly limited ( i have made 2 effects pedals for electric guitar ) but after hearing that my great grandfather ran a radio repair shop and reading/watching things online, I've become interested in the craft. From the back of my cousin's barn me and my dad have managed to retrieve some of his, presumably unfinished, repair jobs including a Bush vhf 61. Possibly very naively, i decided that this seemed a good place to start as the unit is fairly small but spacious enough me to sort of see what's going on in there. I have tried to educate myself one the basic physics of how the components work together and what they do individually, but I'm still apprehensive about putting any electricity into the unit, mainly because it only has a two prong plug which confuses me as someone who isn't familiar with that with appliances without an earth pin. From what I've read this is a common fear which, generally speaking, isn't rational, however I'd rather go into this with a bit more knowledge. Nothing appears to be missing from the chassis but it was very dirty; after removing the valves I tried to brush off the worst of the dirt. I'm aware that the capacitors in old valve amplifiers tend to go bad for one reason or another over time and that they will probably need to be replaced. I am worried that turning on the radio without any prior checking could damage some of the components and cause issues that could be avoided.

My main questions are:

Is the two prong plug safe to use? if not, how should i wire the earth to the chassis?

What can i test before applying power to the circuit? ( I basically only have access to a multi meter )

If parts need to be replaced (capacitors and resistors) where can they be sourced in small quantities?
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Old 4th Aug 2018, 7:33 pm   #2
egerton
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Default Re: Bush VHF61 restoration

It's good to see a young person taking an interest, I hope you will stick with it and have success. I'm sure someone with far more experience than me will answer you here soon, but from what I have learnt so far as a relative newcomer to valve sets, this is my advice -

Make yourself a lamp limiter, very worthwhile for initial power ups - there is information in the forums on this.

The 2 pin plug must be replaced with a standard 3 pin mains plug. I believe this set has a transformer and if so, so you should be able to earth the chassis for added safety. But do seek advice on this because some sets have a "live" chassis and you need to understand this when working on valve sets.

A good place to start may be doing a visual check for obvious problems consulting the forum here, then bring up power on the lamp limiter and if all is well see if the valve heaters are glowing.

Good luck - Paul
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Old 4th Aug 2018, 7:48 pm   #3
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Default Re: Bush VHF61 restoration

This is the manual.
https://www.service-data.com/product...64/1101/m10664

and this is well worth reading and understanding before you start.
https://www.vintage-radio.com/repair...ion/index.html

Treat the radio with respect for your and other people’s safety, voltages can hurt or kill, learn safe working practices and enjoy the hobby.
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Old 7th Aug 2018, 8:17 am   #4
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Default Re: Bush VHF61 restoration

I know the temptation is to get in there & have a look but I would respectfully suggest that you read as much as possible about your particular set & the safety advice here on the forum. I've been in electronics for over 40 years & I've learned a lot from this forum. There is a wealth of good, sound advice & if you are unsure then just ask. Others with far more knowledge than me will be more than willing to offer advice & guidance. Best of luck & keep us informed as to your progress. Best regards.
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Old 7th Aug 2018, 9:05 am   #5
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Default Re: Bush VHF61 restoration

Hi and welcome to this fascinating hobby and to this forum. I think the Bush VHF61 is a good starting point and is capable of giving a really good account of itself.
As others have already said its best to read up on those excellent links first because high voltages demand respect and its always safety first.
Do not be afraid to ask questions and keep us updated on how you are getting on,
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Old 7th Aug 2018, 9:21 am   #6
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Default Re: Bush VHF61 restoration

Learn how to really use your multimeter on all ranges.

Lamp limiter is the way to go, saves blowing fuses, saves damaging things, saves frightening yourself from big BANGS.

The set has a proper isolating transformer so you can put an earth wire onto the chassis and a 13A plug with a 1 amp fuse from the get go. 3A fuse if you can't find a 1A.

The wax tubular capacitors (caps) are suspect as are the small tubular plastic ones that will shed their coatings when touched.
Do not change any flat wax caps, they are silver mica and very rarely faulty.

Don't wade in changing anything, establish if it works as a whole or in part first.
Get the power supply working, then the audio stages then the rest.
Change one part at a time and test that the set still "works" as it did before, this way you find any introduced faults (mistakes) straight away.

At 16 you will get as much help as you ask for, we are really pleased that someone not of pensionable age is interested in this hobby.

If you want bits, ebay is handy but I'll bet if you ask, you will get them from folks here free and gratis.

Sam.
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Old 7th Aug 2018, 1:14 pm   #7
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Default Re: Bush VHF61 restoration

ANY radio with VHF is ambitious for a beginner to start with! It's more complex, more to go wrong, more quirky than an AM-only set. But you may still be lucky with it!

If it is at all decent in condition, I'd suggest find something simpler, just a basic 2 or 3 band AC superhet, Cossor 500 or 501, to learn on.

Safety advice is definitely important. Accept that sometime you WILL give yourself a shock, so first, make sure it is a small one. Table radios rarely have more than 250V available, except in the one place between the anodes of a FW rectifier. Make sure a shock is not across your body and over your heart by working with one hand at a time, which you keep clean and dry; make sure you know when power is on (simple things like replacing dial lamps as one of the first things to do); and avoid consequential injuries such as falling backwards from a stool when startled by a sharp tingle, by working in a safe position in the first place.

Egerton and Boater Sam advocate making a lamp limiter. This is really good advice, and straightforward and inexpensive to set up. When you have made that, you probably are going to have to bite the bullet, plug your radio in, and switch on!

What tests can you do first? You can measure the resistance between the pins on the plug, which should be some tens of ohms (if there is a mains transformer) or some hundreds (if there isn't). You can check the on/off switch at the same time: switched 'off' it should rise to infinity.

There is one capacitor, which is present in the majority of radios, which ought to be replaced as a matter of course: it is the capacitor which feeds the control grid of the output valve. Luckily, the value is not critical, anything from 0.005uF to 0.1uF will do as a temporary measure (though the original value will be best).

There's loads of people on here who will be only too glad to help you to have the fun that they do, and maybe embark on a career in electronics!
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Old 7th Aug 2018, 2:49 pm   #8
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Default 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.
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Old 7th Aug 2018, 3:04 pm   #9
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Default Re: Bush VHF61 restoration

There are many small plastic coated Hunts capacitors in this set that will all need replacing and it's not the easiest to work on as they are all crammed into a pretty small area.

First step is to to take lots of pictures showing the connections of all the components. You will need these when you can't figure out where to solder a new component to!
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Old 7th Aug 2018, 3:25 pm   #10
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Default Re: Bush VHF61 restoration

Quote:
Originally Posted by PJL View Post
There are many small plastic coated Hunts capacitors in this set that will all need replacing and it's not the easiest to work on as they are all crammed into a pretty small area.
That's what I was going to say!

These are great sets and are easy to restore, but there's no way I would have liked to tackle one as a beginner. You need to be a proficient solderer and have the patience of a saint to do the job well. If you skip this bit, performance will be very poor, at best.

Something like a VHF80 or VHF81 is FAR easier to restore, and although you'll have to learn about "live chassis" techniques, they're dirt cheap and brilliant performers too: https://www.vintage-radio.com/manufa...sets/bush.html

N.
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Old 7th Aug 2018, 3:40 pm   #11
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Default Re: Bush VHF61 restoration

I restored a VHF62 last year (same chassis as the VHF61 but in a wooden case rather than a Bakelite one).

The set was originally very deaf on MW/LW and didn't work at all on VHF. Further to the previous two comments replacing the Hunts capacitors (one at a time as suggested earlier) was all that was needed to fix it - when I tested the removed capacitors afterwards every single one was either horribly leaky or just plain broken.

It was worth the effort though - the set is a good performer and with VHF capability is actually still useful.


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Old 7th Aug 2018, 4:04 pm   #12
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Default Re: Bush VHF61 restoration

My experience too.
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Old 7th Aug 2018, 5:15 pm   #13
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Default Re: Bush VHF61 restoration

Those 'orrible Hunts plastic capacitors can be hard to get at. The ones wired from the valve heaters (pins 4 &5 ) to ground (chassis) are not so vital, the set will likely work fine without replacing any of these.

You will need good soldering skills. If you leave the leads of the old component in place and solder the new one to them you will find it easier if a little untidy.
Trying to remove the old leads is tricky, they are fitted through the tags and then wrapped round, sometimes twice.
The builders did this as they made a mechanical joint on every component then soldered the lot.
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Old 7th Aug 2018, 6:12 pm   #14
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Default Re: Bush VHF61 restoration

As others have said, great to see someone your age getting an interest in the repair of these old sets, exactly what the hobby needs!
I would also agree not the easiest set to begin with though - what else do you have in the "heap"? something like a BUSH AC34 or a PYE P75 would be good and give you confidence to start on something more complicated when it works.
Put some pictures up if you like and members can advise which would be good to start off with.
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Old 7th Aug 2018, 7:04 pm   #15
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Default Re: Bush VHF61 restoration

Yes there are lots of Hunts caps and they will all need to be replaced if the set is going to work reliably. However if you just replace the one audio coupling capacitor as previously suggested then try the set you may well get some sound out of it. That is what happened with mine although it took more than that to get the VHF working.
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Old 8th Aug 2018, 4:53 pm   #16
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Default

Hello again, as of right now I've gently cleaned removed the chassis and cleaned the cabinet as well; It all seems to be in pretty good shape. The current plan of action is to remove any of the capacitors that have been suggested in this thread and to order replacements along with the parts needed for the lamp limiter. Then I begin testing!

For those wondering, there were a number of other sets in the heap and potentially a collection of valves and other related equipment, but all that's at home with me now is the VHF61, a Peto Scott H52 and a Pye Fenman.

I've recorded all the Hunts caps to replace. Is it worth replacing all of the paper and wax ones too? I've heard that the small caps generally don't malfunction, but is it worth replacing them anyway? Also, is 400V adequate for all capacitors in the circuit?
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Old 10th Aug 2018, 10:58 am   #17
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Default Re: Bush VHF61 restoration

A 400 V voltage rating should be adequate for the replacement Hunts capacitors.

It's best not to replace smaller value capacitors in the set (ie leave anything below 1000 pF = 1 nF undisturbed) as the value of these components are often critical and replacement ones can affect the set's alignment. As you say the smaller value capacitors generally last well - I have yet to need to change one.


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Old 10th Aug 2018, 11:27 am   #18
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Default Re: Bush VHF61 restoration

C60 Bush service manual needs to be 300VAC, replace that with a 1000VDC type, 400VDC in that location across the sound output transformer is a bit too small. C57 would be better with a 630VDC type.
Otherwise 400VDC are fine and take note of Ed's advice on not disturbing the smaller capacitors. In the unlikely event of one being faulty, that can be dealt with later.
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Old 10th Aug 2018, 1:00 pm   #19
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Default Re: Bush VHF61 restoration

Quote:
Originally Posted by sprdsht View Post
The current plan of action is to remove any of the capacitors that have been suggested in this thread and to order replacements along with the parts needed for the lamp limiter. Then I begin testing!
You don't remove any capacitors at this stage. Make your lamp limiter and power it up with that first so that you know the state of play before you start. Only then do you assess what capacitors you need to replace. There are several critical ones such as the grid coupling capacitor as has been mentioned. Then there's a couple on the AGC line that should ideally be replaced. The rest of the Hunts can probably be left, as they're not in critical positions and any leakage they have won't stop the set working or cause any damage - it's up to you.

If you start removing and replacing parts before basic testing, you won't know whether there's any failed parts such as transformers that may make the set beyond repair, also you may introduce faults that weren't there before, so TESTING FIRST!
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Old 10th Aug 2018, 5:55 pm   #20
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Default Re: Bush VHF61 restoration

Quote:
Originally Posted by Boater Sam View Post
Lamp limiter is the way to go, saves blowing fuses, saves damaging things, saves frightening yourself from big BANGS.


Do not change any flat wax caps, they are silver mica and very rarely faulty.

Don't wade in changing anything, establish if it works as a whole or in part first.
Get the power supply working, then the audio stages then the rest.
Change one part at a time and test that the set still "works" as it did before, this way you find any introduced faults (mistakes) straight away.



Sam.
OK? I'll say it again in case you missed it, get it working first.

Sam.
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