EP 146 - Zetagi BV 131 - Valve amp - Repair and test. 

I'm a bit late to this party, as I haven't looked in on your channel for a few months. I'm also a C&G fully qualified 'old school' TV engineer and have worked on loads of these BV131 amplifiers and enjoyed your video. They work extremely well, but are only good for short duty cycle DX, and not for general yapping on UK FM. I've seen them with the watt meter totally melted from radiated heat from the valve - I always used to fit a heat shield to protect it. I've also fitted small cooling fans below the valve, drawing cool air in from below, but it's a bit of a 'faff'. I once fitted one to only work when RF was present, so it wasn't whirring away all the time on idle, although I think if you're going to fit a fan that it's probably better to have it running all the time regardless, as there's a lot of heat to get rid of and fans are made to be quieter now than when I used to fit them back in the 80s. You're very lucky on a couple of counts with that amplifier, one being that the mains transformer isn't burnt out - they often are, due to that radiated heat and the fact that most of them are wound for 220 volt mains and not 240 volts - a check of the heater voltage will confirm, in that if it's over 6.3 volts by a good margin (like nearer 7 volts), then it's a 220 volt transformer and likely to have a short life, as too will the poor old valve. The second thing that you were lucky with is that it's the EL519 and not the earlier 6KD6 version, which melt their RF chokes and also the valves are near on impossible to find at a sensible price nowadays, also the 12 pin valve bases arc and burn out and are impossible to find. It's funny that those main HT doubler capacitors are nearly always a bit leaky from the ends, but it doesn't seem to bother them, although those in your amp are definitely the worst I've seen, so not a bad idea that you replaced them, although I've never known one to actually fail, which can't be said for a few of the others on that board, basically all the ones you didn't actually change, but you just take a chance, as even replacements can fail a week later due to the stress they're under. The whole amplifier is run under a lot of stress and you have to expect component failure. Those pentode valves are triode strapped and run in grounded grid mode and that original valve could potentially lose several of its other pins and still work, but unfortunately it looked like it was the cathode pin 9 that was broken off on your valve and it's only got one of those, so it was unfortunately finished! There's no HT when you first switch the unit on and let the valve heater warm up, so there would be no potential 'bang' until you actually applied RF, and there we come to the other very common failure, and that's the RF sensing relay switching transistor (2N2222 or similar), which I used to make a little heatsink for to increase its reliability. I've never known those HT doubler rectifier diodes fail, although there's always a first time. You need to tune the front control for maximum RF output immediately on applying RF, or the valve will have a short life. I don't have the time or inclination to work on these things these days, although an old friend has dropped one on me to look at a while ago and it's got the usual burnt out transformer and duff valve. I've tested its potential working state with my large external testing transformer, so I know it's capable of working with a rewound transformer and a new valve, but whether it's worth the expense is another matter. Are they good RF amplifiers? Yes, they're very good and they work in a proper class of operation that doesn't 'clip' on AM and SSB. The problem is that they're run on overload and tend to have a very brilliant, but short life, particularly if hammered on UK FM, the whole anode structure of the valve can be seen to glow bright red - that's when your watt meter melts and drops out of the front and the transformer goes up in smoke...lots of stories of this happening back in the day! Is there a better amplifier of this class for general use? Yes, but unfortunately it's the B132 single transistor version. These 'look' like the BV131 and use the same metalwork, but are a basic X10 amplifier - 4 watts in, 40 watts out, 10 watts in, 100 watts out etc. They'll run all day every day and are very reliable, the only faults I've had are the relay contacts and the main single power supply smoothing capacitor going open circuit (or severe lack of capacitance), they also don't 'clip' much (if at all) on SSB, so a good all rounder. They'll run for hours with 12 watts in on SSB and hardly feel warm to the touch on the rear heatsink, but keep FM to 4 watts if you have long overs! Is the Bremi BRL200 any good? Well yes and no. It's more reliable but doesn't have the 'poke' of the 131 and the valves are getting difficult and expensive to source, having not been manufactured for decades. If you want a real challenge then get a BRL500 - at least they use the EL519, five of them in total and I've always bought the Russian 6P45S/EL509 from sellers in Ukraine at sensible prices, but I have to say not recently.

I had one of these in the late 80's, wish I'd kept it. First time I've seen inside one, very interesting.

Nice looking unit mate

I had an amplifier like this one years ago great video and nice to see you back mate

Absolutely brilliant video

happy new year graham. I think i have the 2 valve BV135s in a box in a shed. Nice service on this nice old bit of kit.

Graham a H.V internal fuse in the anode lead between the last 47uF electro and the plate inductor would not go a miss ,one in the filament also if you need spare el509's i have some good to see you putting bleeders in certainly a must in cb type amps

Great to see you working on valve gear. I would love to watch you tune a cobra 148, miss Mark the cobraman doing all that stuff

Graham, it's great to watch your video. I'm a bit of an anorak for old CB tube amps. I think I may have seen that russian valve before. I've not watched any of your content before, but I'm certainly going to be watching from now. RG 205 Kevan Swansea Wales

This is my favourite version of the bv131 i use the russian tubes in mine.

happy new year graham , god thats a blast from the past the old zetagi BV131 solid as a tank , i have one here i need to check out . i also have its compedtitor the bremi BRL200 thats a beast that one lol .its great to see you reviving the old school equipment far better than some of these modern cb radios . i find it really theapeutic watching your videos most enjoyable . keep up the fab videos and work all the best ,mark

HNY Chap

Hello, thank you for this great video. I would like to know the value of the overvoltage resistors on the 47uf 500 capacitors. And also the value of the diodes below the capacitors. Thanks in advance. Sincerely

Trying to fix a Bremi BRL200 amp. All ready to roll but won't switch into TX - I think it may be transistor 2n2222 ?

No bleeder resistors either! 😱