FREEBANDING

I'm no expert in electronics, far from it. Twenty year ago I used to muck about with radio and radio ancillaries, but over the years the knowledge has been forgotten, not used. Even then, years ago, I would never have called myself an expert, it started with fitting microphone plugs for people, then they started to come round with broken radios. I had some rudimentary equipment, I could change frequencies, expand rigs ,fix them, I had started to understand how it all worked. Then I stopped and went onto something else until now.

I started to get back into radio and as I did I found some of the interest in "how it works" returning. I have been frustrated as I just do not remember much at all about electronics and radio. But, recently I have been reading a lot about the technical side, I have found myself saying "oh yeah, I knew that".

I had a RM KL400 linear that I damaged by using it over a wider range of bands, which it should be able to do but without going into too much detail I bust it. At the time I just put in in a box under the bench. Then I bought a RM KL500 linear amplifier, but that got damaged in the post. So I decided to make one good linear out of the two, but I just did'nt have the knowledge. I do now and it seems that the transistors have failed in both linears and the damage may have been a cover up for selling me a duff linear. Shelved.

Without going into too much detail I have bought, and sold, several valve linears since.

I dont really need a linear amplifier, I have a good antenna and 100 watts from the radio, generally I can work what I hear.

But I bought one anyway, a Bremi BRL 500. Its a 500 watt valve amplifier that looked ok. I bought it from Ebay for seventy five quid from a bloke who's feedback seemed ok and the unit looked in the photos reasonable. These are the pictures as it was advertised:

I picked it up from Dartford on my way down to a family get together, when I got home the first thing I did was put a plug on it and try it. It failed, it really failed. It lit up, four of the five valves glowed, all the switches seemed to work but zilch power and a relay was arcing out like mad somewhere inside.

Right then what to do with it? Well it cost me seventy five quid so I'm not throwing it away, I done fancy sticking the blimin great heavy thing under the bench with the other two broken linears, becoming a bit of a linear graveyard around here.

First thing was to read up on the unit and get a wiring diagram and schematic. I hit the Internet and had no luck what-so-ever. To this day I have no information on this amp at all, if you have some then I will be very grateful if you would send it. Anything even an advertising leaflet would be more than I have.

I have done some research with regard to valve amplifiers, coupled together with a sparse and forgotten knowledge of something to do with radios I have started to restore this beauty.

The valve that's missing was there but just fell to bits, oh dear I went further into the unit

The capacitors had some leakage residue on them, so they will need changing, I found the arcing relay and removed that as well with a view to replacing it

I took the out casing to work and gave it a paint job and some new feet, for the first part of the restoration project

Then I thought about spending some money, now I cant afford to buy loads of bits for it and discover it's completely knackered, so I managed to find a valve supplier and bought just one valve. Then I sort of fitted the valve. Because the valves are soldered in I bodged up a method of fitting the new valve without permanently fitting it by using the old valve cap on top of the new one.

I powered up the unit, let it warm right up. I put four watts into it and got one hundred out. Only the new valve is working. This test was a great success as I now know the major fault is with the valves and now I need to buy the other four. I know it works, I know it has power supply, I know it can be fixed. But it will cost about another hundred quid so it will have to wait until after Christmas.

More to follow, while I'm saving up for four new valves, I'm going to clean it up inside, tidy up the wiring and some of the soldered joints, try and figure out why the meter doesn't work, change the capacitors and the light bulbs, tidy the face up and fit new knobs, clean as many electronic connections as I can and above all sort out some of the crap soldering.

I ordered the valves from a source in the Ukraine, they took eight days to arrive and that was with Christmas in between, they dont look the same, they are fatter and have some weird numbers in Russian on the side. Oh well, if they're wrong they're wrong the base is the same so in they go.

Here's and image of the unit waiting for the valves, all clean de-soldered, and tidied up.

I put the new valves in and made a good neat job of soldering them in place, much better than the previous job.

Put it all back together ready for the moment of glory or disappointment. I was that confident I put the lid on and all the screws in. But my confidence was misplaced.

When I tried it the relay was arcing really bad and with no output at all from the valves. Bum. So disconnect all the leads, remove all the screws and take the lid off and try some investigation. I was a little worried it was the transformer, remember I don't have any information on the unit, none, so I was guessing. After measuring some voltages that appeared to be correct, if not lower than I have been lead to believe. I split the unit in half again.

There on the edge of the power supply board was a tiny thin wire poorly connect to the pcb. Not confident this was the fault I re-soldered it in place. Also I traced it to the relay for TX switching?

This time I tried it with the lid off, I was going to be careful as I realise it very dangerous.

Bingo! 300watts. Ok we can do better than that. It seems the tuning capacitor on the load side is not working so first job to make sure the plates are not touching, then clean off the crap in between the plates. Try again, wallop! BANG. Crikey what on earth was that? I thought.

Check the obvious first, the fuse had blown, but in spectacular style. It seems the fuse is a modified 13amp fuse in a poor condition holder. This had arced out and caused the flash bang wallop. New fuse then, stand back and try again.

Full 500w with ten watts in! Wooohoo it works. Get a radio check from a local station and superb its works perfect. Put in all back together and we have a fully operational Bremi BRL 500 valve linear amplifier for the 11 metre band.