Custom 50 (1981) - post repair advice

[jinglejangle]

A bunch of info on my amp is at this previous thread:
viewtopic.php?f=2&t=2177

My main questions regarding the info below the break: Is the repair cost fair? What could cause this sort of hum? Since there's a chance the hum was introduced by the tech with the repairs made, should I request that the cost be encapsulated in the previous repair bill (free this time), or is that just insulting? These repairs are expensive and I can't sink another $100+ into the amp when the issue wasn't even present in the first place (guessing the tech is going to want me pay for more bench time). IMO the tech should have recognized the hum and fixed it. Any suggestions for Philly based techs?

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I bought a Hiwatt Custom 50 (Hylight, 1981, circuit board) in January of last year. It sounded great from the beginning so I played it, even though it looked dirty and in need of service. I played it with an attenuator and regularly cranked the amp for about a month. One night the volume dropped out and the amp started to smoke.

I finally got the amp repaired and to be honest, I'm disappointed. Here's the breakdown of the repair:
Hourly charge - $90 per hour and then $80 every hour after.
- Replace (1) dual can(?) filter cap
- (1) 1K 5w resistor
- (1) 10k 2w resistor
- Dremel burned circuit board (was told this is necessary due to conductive carbon being embedded in the board)
- Repair Normal input jack (a washer or something was missing)
- Retension sockets and clean controls etc.
- Test tubes - OK
Cost: 282.50
Tax: 16.95
Total: 299.45

I was a little shocked at the price. I called around before I landed on this tech and most techs advised that repair costs rarely went over $200. Regardless, I was fine with it because I figured the repair should last at least a few years. I tried to ask why the cost was so high and the tech just said "well I had to take out the board."

I get the amp home and it sounds great, but now there's a constant, low-level hum. I'm almost certain the hum wasn't present before - I remember comparing the Hiwatt with my Fender Bassbreaker 15 and I was surprised by how quiet the amp was at low volumes considering the wattage difference. There definitely wasn't a constant hum present.

Audio of hum: https://1drv.ms/u/s!Ah2NF4UfbNDOkBMB4iZ ... Q?e=7EvsEb

The hum is constant regardless of where the amp is plugged in, the volume of the amp, or which input is being used. Basically with all controls completely turned down the hum is present. The only time it's not present in when the amp is in standby.

Thanks to anyone that reads this and provides input.

[mhuss]

That sounds ominously like the output tubes red-plating. At night, get it making that sound, turn off the lights, and look at the output tubes. The heaters will be glowing orange, but the larger metal parts should not be.

(Every time I read these stories, I think "darn, I don't charge enough for repairs." Sigh.)

[jinglejangle]

That sounds ominously like the output tubes red-plating. At night, get it making that sound, turn off the lights, and look at the output tubes. The heaters will be glowing orange, but the larger metal parts should not be.

(Every time I read these stories, I think "darn, I don't charge enough for repairs." Sigh.)

Thanks for the advice. I really hope not, they are the original Mullards. I checked them a few times and didn't see any red-plating, but I'll take the back off and see if I notice anything. The amp in general seems to be getting hotter than it used to. I touched the front plate and it was very warm. I don't remember it getting that hot before the repair. I also noticed a "hot electronics(?)" smell, which I assumed was due to the amp re-acclimatizing after the repair. I was super paranoid when I smelled it and immediately checked the output tubes which seemed to be glowing brighter than normal and hotter than normal. You wouldn't happen to have a picture of some glowing Mullards in the back of Custom 50 for comparison?

[mhuss]

No picture, but it is often a very dull orange glow, right in the middle of the tube (not at the top or bottom). It can be hard to see in normal light.

[OldSchoolDave]

Any suggestions for Philly based techs?

I can't think of anyone more qualified than mhuss...

Try swapping the power tubes with a cheap pair (eg. JJ E34L) to see if conditions change. Unfortunately, your Mullards may have already been damaged, but there's no sense in risking anything further.

If you have access to something like a Weber Bias Rite, you'd know in short order whether the voltages are too high. Testing Bias the Old School way can be dangerous and should be left to professionals.

Good luck,
Dave

[mhuss]

I'm about 30 miles West of Philly, near Coatesville.