long story:
About 7 years ago a colleague in work asked me if I wanted his old guitar combo. He'd been sorting out his attic and found it and rather than chuck it away he thought he'd offer it to me. I went to his house to get it and he handed me a Guyatone GA-620, looked like a copy of a Fender Princeton Reverb, he told me it hadn't been switched on since sometime in the 70s. I took it to a guy in Bristol for him to switch it on for the first time, I didn't fancy the risk of electrocution. Brizzle guy replaced a couple of dead capacitors in the output and power sections, and replaced all the valves.
When I got it home I found that the volume didn't really work, neither did the tone controls.. nor the reverb and erm tremolo... But there was sound and it sounded good. So I got on the internet and tried to search for info on the amp. But the only results to to photos of it I'd uploaded the day I'd got it. Life got in the way and the combo was put aside. A few years ago I decided to see if I could revive it. In the years that had past someone had sold the same combo on reverb.com and had uploaded quite a few photos, including a schematic! Not having the time to deal with it I printed the schematics and took the amp to a repair place in Cardiff. He had it for 3 weeks before telling me it wasn't worth repairing. I disagreed and asked what needed to be done. His reply was "buy a new amp". Not being one for defeat and being fairly handy with a soldering iron I went off and researched amp repairs.
Last year I replaced all the dead oil in paper capacitors and lo and behold the treble control and volume started working. The bass control had a very minimal effect, but neither the reverb nor tremolo came to life. I bought another new complete set of valves, I then noticed that one of the valves was the wrong type. Stuck in the correct one and the tremolo fired up! I traced the issue with the reverb down to a dead driver transformer and the bass tone control was wired nothing like the schematic was laid out. So I put it back to how it should be, but still it was a bit ineffective. But the amp worked better and sounded awesome, but got noisy after about 20 mins. I replaced some of the valve bases as they were a bit knackered looking.
Life got in the way again. Then last week a post on a facebook group alerted me to a tech who lived a 2 minute drive from me. Yesterday I called him up, "Bring it round now if you can" he said, "It'll save me from having to repaint my kitchen!"
So off I went. Rather than leave the amp with him he started working on it as I gave him the above history. He checked the reverb driver transformer and it had indeed died. So he replaced it and replaced a suspect ground wire. Tested it and the amp now had a fantastic sounding spring reverb. It then took 2 and a 1/2 hours to diagnose the trouble with the bass control. Who ever had altered the circuit had also got the two capacitors on the wrong sides of the pot.
Tech guy then said the noise, once the amp was warm, was a 95% probability of some of the old resistors going out when warm. He told me the best way to find which were causing the problem. He said he wouldn't do it for me as I'd obviously spent a fair amount of time sorting things myself and getting to know the amp.
At this point in time I've spent about £100 in total on the combo, including over 3 hours of time and a transformer from the tech yesterday. About another £20 for some new resistors and the amp with be sorted. It sounds so good. Razor sharp highs and warm lows...
It's been a long journey, that's not yet over, but I've learnt quite a lot about amps...
