1978 HD130 Head just before changover new series

pleiksnal

Hello,

I've recently acquired one of the transition model HD 130 musicman with the transistor preamp.

Unfortunetely the amp doesn't work properly even after doing a cap job. I knew there were issues with the amp when I purchased it which is why it was cheap. It didn't seem like it had the symptoms of a blown transformer.

The amp has a very light fizzy, farty sound when I strum the guitar fairly hard so there is really no tone atm. I replaced all the main caps and it still sounds the same as before.

Could this be a transformer issue? I know that the valves are fine and they are glowing nicely. I also notice the standby severly flickering in intervals. This is especially noticable when its on the high mode. Low mode has less flickering.

Has anyone else had an issue like this before?

Thanks
Levi Pleiksna

Music Man Equipment
MM 2-10-65

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11 years 2 months
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mm210 Thu, 09/11/2014 - 09:27

Have you checked all of the voltages in comparison to the schem? That should be item one. Check for high voltage readings on the finals and the plus and minus 16v on the preamp side. We'll start there.

Full Name
Sean
Music Man Equipment
1979 212 Sixty-Five, 1981 212 Seventy-Five
Numerous other amps and several guitars...

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11 years 2 months

codamedia Sat, 09/13/2014 - 05:24

I'll deal with the light, and leave the real problem to Mike :)

Are you saying the on/off light is flickering? If so, I would not be alarmed about that. IIRC these are neon, and they simply die slowly over time (eg: flicker) rather than burn out like a regular bulb. On the early Musicman amps the manual even stated that the light may not work under certain conditions. One of my Musicmans has been flickering for 15 years... one of these days I will buy the .75 cent part to fix it - LOL!

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11 years 2 months
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mm210 Sun, 09/14/2014 - 04:52

After checking voltages, if they are all OK, and ASSUMING the tubes are good, I'd go with bad drivers in the driver board. Remember, this is just a SWAG! Mike.

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

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11 years 2 months

lmv Sun, 09/14/2014 - 12:38

Hi there, is the fizz sound in the background of the sound? Sorta like hearing a distorted ghost note behind the real guitar note?

Sincerely,
Lars Verholt

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Levi Pleiksna

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11 years 2 months

pleiksnal Wed, 09/17/2014 - 01:13

Wanted to give you a direct reply because you have had the same problem by the sounds... There is no real note though just the ghost note :/

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

Member for

11 years 2 months

lmv Wed, 09/17/2014 - 05:37

It's a distinct possibility that you have some crossover distortion. This can happen either due to bias being set too cold or there is a defective part somewhere. A leaking coupling capacitor, for example, could introduce this problem. In your amp we're talking C35 and C36 both 20uF/25V.

Sincerely
Lars Verholt

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Levi Pleiksna

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11 years 2 months

pleiksnal Wed, 09/17/2014 - 01:12

Thanks for your replys guys and sorry about the late reply. Mike I will check these first up. Which schematic are you referring to?

Lars that is exactly what it sounds like, I couldn't have described it better! Are you an author?

LP

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MM 2-10-65

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11 years 2 months
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mm210 Wed, 09/17/2014 - 12:00

Listen to Lars!

Full Name
Lars Verholt
Music Man Equipment
HD-130 head, 210X cab, 210RH cab, RD-50 110 combo, Sixty-Five 112 combo, RP65-112

Member for

11 years 2 months

lmv Fri, 09/19/2014 - 05:39

"Fizz is for tonic water, not for amps"