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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 1st May 2017, 10:23 am   #21
Michael Maurice
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Default Re: Ultra 6322 Radiogram restoration

I tried that once and it didn't work. The AF12... are not that expensive.
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Old 1st May 2017, 11:00 am   #22
Edward Huggins
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Default Re: Ultra 6322 Radiogram restoration

Yes, that's definately a Garrard 3000, but with an Autoslim platter - but that slightly oversized mat is not from an Autoslim. A great step-by-step report Indy! The Garrard 3000 tone arm and the Sonotone 9TA/HC is an ideal combination.
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Old 1st May 2017, 11:07 am   #23
'LIVEWIRE?'
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Default Re: Ultra 6322 Radiogram restoration

As I noted in post #10, Russian Germanium transistors in to-72 encapsulation, type GT322A, like AF127s, but pinouts as per AF139s (base & emitter connections opposite to those of the 127) are usually available on eBay. They have the advantage of longer leads (about 25mm) than 127s, which makes them easier to fit in place of AF11x transistors than AF12x types. I don't have a data sheet to hand, but, AFAIK, they can be used at up to VHF, certainly up to 10.7Mhz. (Ft 80Mhz. Vcb 25v, IC 10mA acc to data on eBay, so can replace AF124-127, and, AFAIK also AF114-117. I've used the GT322A on several occasions, most recently in a Perdio 'Caralux' without having to make any circuit changes. There are currently two eBay sellers offering packs of these transistors.

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Old 1st May 2017, 11:10 am   #24
paulsherwin
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Default Re: Ultra 6322 Radiogram restoration

It's a myth that BF450s are some sort of magic substitute. My advice would be to try a 2N3906 or BC558 - if they don't work then no silicon transistor is likely to (without circuit changes). You can buy 100 Chinese 2N3906s for 99p including postage.
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Old 1st May 2017, 11:51 am   #25
indigo.girl
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Default Re: Ultra 6322 Radiogram restoration

Thanks Livewire and Paul - Think I'll give the cheap and cheerful 2N3906 a try first. If these don't do the job I'll consider the more expensive GT322A's. Will report back with results soon
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Old 1st May 2017, 1:37 pm   #26
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Default Re: Ultra 6322 Radiogram restoration

If you just want a few to try out you can buy them over the counter from Maplins - they cost more than 1p each there but are still cheap. In the longer term it's worth ordering a stock of 2N3904s (NPN) and 2N3906s (PNP) from China as they are versatile general purpose devices which will sub for a wide range of other types. Some suppliers will send 50 of each for 99p.

https://en.wikipedia.org/wiki/2N3904
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Old 1st May 2017, 4:00 pm   #27
indigo.girl
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Default Re: Ultra 6322 Radiogram restoration

Fantastic - How versatile are these? Could I in theory use the PNP and NPN versions for all replacements in a normal transistor radio receiver / amp circuit?
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Old 1st May 2017, 4:11 pm   #28
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Default Re: Ultra 6322 Radiogram restoration

The 2N3904 and 2N3906 are low power transistors, so you couldn't use them in the output stage of a powerful amplifier (they probably would be OK in the output stage of a small portable radio). And they're not really high frequency parts, so I am not sure they would be good in the 'front end' of an FM receiver.

But they would probably do most jobs in an audio preamplfier, AM radio, etc. FWIW they are also a replacement for the power converter transistor in old HP calculators.

[True story. I once had to repair a Tektronix spectrum analyser plug-in that had suffered a major blow-up when 2 power rails got shorted together. Just to see how bad it was, I replaced all NPN transistors with 2N3904s and all PNP wth 2N3906s. It worked perfectly, and seemed to be still in calibration. Of course I didn't leave it like that, but it shows how versatile these transistors are.]
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Old 1st May 2017, 9:37 pm   #29
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Default Re: Ultra 6322 Radiogram restoration

They will usually replace all the silicon transistors in a radio (including BF194/195 RF Lockfits) apart from the output transistors. For a low output radio you can use a 2N2222 / 2N2907 pair for output, though if the radio is a powerful one then a 2SB772 / 2SD882 pair would be better. All these general purpose types are available for pennies from Chinese suppliers, but will take a few weeks to arrive.

There are many other general purpose types which can be used, but these are some of the cheapest.

Replacing germanium types with silicon is trickier because the operating conditions of Ge and Si are different. You can often replace an AF117 or OC71 with a 2N3906 or BC558 without problems, but it's not guaranteed to work (or work well). If you change an AC128 / AC176 output pair to silicon you will almost certainly need to modify the circuit to get it to operate properly.
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Old 14th May 2017, 6:35 pm   #30
indigo.girl
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Default Re: Ultra 6322 Radiogram restoration

UPDATE: I have replaced VT3 to VT6 with 2N3906's as suggested and its been a great success. The AM channels have not sprung into life in addition to the FM. Not only that but the HT values have all increased up to spec values (slightly above actually). I was previously only getting 5V feeding the RF amp/osc/mixer sections but now I get the full amount. So, something was obviously not quite right with not only VT4.

Curiously though this has also had a knock-on effect of solving my over-sensitivity issue with the gram pick-up. I was finding that the amplification was so high even at low volume setting that I had to reduce the signal by 1/3 with a couple of resistors. This problem is now gone. I have no idea how this has happened since the transistors that I have replaced are not involved in the gram circuit. Very strange - but fortunate
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