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More noises on my 212 HD 130 with Audio Sample

Hello everyone,

I play a 1970s 212 HD 130 with the 12ax7 phase inverter.

I posted a few months ago about an intermittent static issue I was getting. I seemed to resolve that issue by re-flowing the solder connections on a few suspicious looking spots.

The amp has been playing relatively well since then. However, I have recently noticed a new sound creeping up every now and then. It's pretty annoying. It's kind of like static or fizz that breaks through the normal signal. The static I was getting before showed up regardless of whether I was playing or not. This static seems only to appear when I play.

Follow this link to hear a sample I recorded:

Noise can be heard from about 3 seconds to 10 seconds.
At 35 seconds I switch from low power to high power.
Noise can be heard again from around 41 seconds to 52 seconds; 1:36 seconds to 1:38 seconds; and at other times til the clip ends.

I would love to hear from those with more experience if you've ever heard a noise like this before. It may help save me a little time trying to diagnose it myself.

My guess for now may be a bias issue. I notice that my bias reading fluctuates from .50 down to .492 and up to .530 sometimes. Is it normal to see the bias fluctuate like that?

I have materials here to create a signal tracer. That may be my next adventure.

Any other thoughts or suggestions would be appreciated! Thank you!



I couldn't hear any fuzz or noise, but my ears are old and may need waxing. The bias voltage fluctuations looked OK (5%) for an un-regulated power supply. When was the last time it was cleaned and serviced? How old are the power supply caps? Maybe look for more bad solder joints and clean the tube sockets. Love the fat reverb BTW. -mgriffin


Thank you for the feedback!

Thank you for the feedback!

The noise I'm referring to appears at the beginning of the attack of my guitar signal. It's a fizzly, ripping, static like sound that quickly disappears. It almost sounds like a sparkler or the fizzy sound a roman candle makes when it goes off.

I had it serviced last Fall, but I wasn't happy with how it sounded when it came back. Buzzy, hummy, and the tubes seemed to run really hot and produce an overheated smell. I decided to use this amp as a way to learn more about amp repair and maintenance. I've done quite a bit to it the last six months or so.

It has new power supply capacitors, filter capacitors, and electrolytic capacitors as of January 2020. I replaced the bias potentiometer, the 620 ohm resistors and diodes around it (the board looked a little cooked in that area). New tubes as of March (matched quad of JJ E34Ls). I put in new LM307H opamps on the main board for channel 2. I replaced the Zener diodes on the main board. I've replaced the capacitors on the driver board. Replaced a couple capacitors on the tube sockets. A few other things too. This thing was pretty beat up when I got it and has made all kinds of weird noises every now and then. It's been fun to breathe new life into it, but it's caused a few headaches as well.

So, with all that having been done, it may just be a bad solder connection somewhere.

It might also be my guitar's shielding! Playing through it tonight, it sounds pretty good, but I have one guitar that builds up static. I noticed the sound when playing through that guitar.

Thanks for the feedback regarding the fluctuation in the bias reading. I'll keep that in mind going forward.


Quick update: I determined

Quick update: I determined that this noise is (most likely) NOT a guitar shielding or static-build up issue. Played with two well-shielded guitars tonight and heard the same noise again.



Have you run the amp through a different speaker? -mgriffin



I played through a different set of speakers and the noise didn't show up. The noise is sometimes pretty sporadic, so that test may not really determine anything. Also, I'm playing through a new set of speakers in the amp, so I don't think the speakers are the culprit.

Other updates:
- I reflowed the solder connections on the driver board. After doing this, the noise has still appeared from time to time.
- I've been able to "catch" the sound coming through channel 2 rather than through channel 1.
- The tremolo and reverb footswitch rca jacks are suspect. The reverb jack makes lots of noise if I jostle the footswitch input, even to the point of cutting the reverb completely out. Bad RCA jack?
- The tremolo rate will change on its own after I work on the amp. I have to adjust the internal trim pot to get back to normal.

Don't know if those last two issues have anything to do with the original issue, but thought I'd add it to the list of observations!

The amp sounds great like 95% of the time. It's that last 5% that drives me crazy. Hopefully I'm not chasing ghosts!


Quick update on the reverb:

Quick update on the reverb: It's a bad footswitch connection, not a bad rca jack.


Good work.

Good work. I think you've figured it out. How does it sound on Channel 2 with the foot switch disconnected? -mgriffin


Plays like a dream

Played it the last fifteen minutes or so with no issues. Plays like a dream. Clean, overdriven, and fuzzed out. I'm hoping the footswitch is indeed the culprit. If it's not, I'll be back! Thanks for the guidance, mgriffin!


Back to the drawing board

Playing this afternoon without the footswitch and the sound returned. I was playing with an overdrive and delay pedal through channel 2 when it started. I quickly switched over to channel 1, but could not duplicate the noise through channel 1.

Time for a good tech? Any recommendations?


Input Jack?

Sorry you're still chasing a gremlin. Are the Channel 2 input jacks in good shape? IE good spring tension, clean and free of rust, good solder joints, mounting nuts tight? Does the noise happen on both inputs of Channel 2? -mgriffin


The Gremlin

Thanks for the suggestion. The noise appears through both inputs in channel 2. I checked out both input jacks on channel 2 (and those on channel 1 for good measure). To my eye, they appeared to be fine. I scrubbed them good with some De-oxit as well. Put it all back together, fired it up, sounded good for a while and then the sound reappeared.

So, I threw in the towel, called an amp repair tech in the closest big city and plan to drop it off tomorrow. 1 to 2 week turnaround time, so I hope to have an update for you then.

Thanks again, mgriffin, for the helpful suggestions. Stay tuned for more.


2475-130 Biasing problem

Hello Forum:
Troubleshooting a 2475-130 amplifier w/solid-state driver transistors, and found one of four tubes shorted out. Replaced all four power tubes (6CA7 JJ quad matched) and still unable to bias amp. Replaced the high voltage flyback diodes, and both 470pF HV caps, and now able to bias up the amplifier (25mV across each 3.9 Ohm Resistors). I'm now getting a white noise "hiss" from the amplifier, and it increases in volume when I turn up the channel volume controls. Set master volume at "5", and adjust each channel. Noise increases or decreases with channel volume. Also, tried channel volumes set a zero, and reverb and vibrato off. Increase master volume - noise apparently increases with the master volume. So without a signal tracer, seems that the white noise is coming from the power section of the amp. The op-amp is an RC4558, and not the 1458. Can i use a NE5532 low noise op-amp,and see if in fact the noise is coming from here. All comments and suggestions are thankful.


Why not?

You can try it. It won't hurt the amp. Don't be surprised if it doesn't solve the hiss issue. Is the hiss loud with a guitar plugged in? Is the Treble cranked up to 10 and the Bright switch ON? Try shorting the Input jack and see if the hiss goes down. Try removing IC7 (if in a socket) and see if the hiss goes away. If yes, the output stage is not the source of the hiss. Put IC7 back in and work back through the pre-amp stage. Remove IC2 and repeat. Let us know what you find. Good luck. -mgriffin

Bob Goodman

Same here

Hey I have a very similar issue greatlakesurf. I have a 1978 410 HD with 12AX7 Phase inverter and original eminence A10-G-HD speakers. The noise occurs when I play with my les Paul Seymour Duncan pearly gates neck humbucker. The powerful attack of the neck humbucker pushes the amp somehow and causes a fuzz/crackling noise (like an unpleasant distortion sound) that starts on the attack and quickly dissipates within a few seconds. The same type of noise will occur when it is pushed by too much reverb or delay but the main culprit is humbucker pickups (bridge as well somewhat but mostly the neck humbucker). Maybe this is why your noise is happening a lot greatlakesurf, because you had heavy reverb going into the amp? (I’m not sure if that was amp reverb or a pedal*)

This occurs when plugged straight into the amp as well as through my pedalboard. The noise is also exaggerated when I scoop the mids on my eq pedal making the guitar even more bass heavy.

I had the amp serviced like 4 years ago and the tech said I didn’t need to replace anything but I needed to replace a broken tube so I got JJ EL34 Ls. I’m not sure if the crackling happened before the servicing because I didn’t know the amp well enough back then.

The noise doesn’t occur (barely at all) with my strat or tele single coils (but I can make it happen ever so faintly with these single coils when I strum really hard with the bass pickups) and similarly, it doesn’t happen much with my split coil les paul humbuckers but it does more so than the strat or tele with these les paul humbucker split coils.

When I turn down the “volume” control on the amp to lower preamp gain (or solid state gain, whatever that gain is) the noise gets lower but is still definitely there too much. The noise also occurs on all inputs as well as on low and high power, 4 ohm, 8 ohm, and the speaker jack switched. I haven’t tested other cabs or speakers but greatlakesurf said that wasn’t his issue.

So in summary, the amp currently isn’t happy being pushed by high output pickups.

Do you have any word on if you got it fixed or not? Thanks!

Also if anyone has anything to add after hearing my comment, please do!

Bob Goodman

Same here continued...

I just turned down my volume pedal for the les paul going into the amp and compensated by upping the amp volume and it fixed the issue. So my solution is to just turn my les paul down before it gets to the amp. Nice.

In the HD-130 manual it says, “The number one jack is the high-gain input... and will accommodate .5 volts r.m.s. input voltage which is considerably more than the strongest pickups.”

I wonder why this unpleasant initial attack-based breakup could be happening.



Bob Goodman

Same here continued...

This guy here tested the output voltages of various pickups. He got .932 volts with his neck humbucker (nearly 1 volt of output). Am I right in thinking that the humbucker has too much input voltage for the HD-130 since it’s above .5 volts rms? .932 peak volts is apparently .659 volts rms. I’m not experienced with electronics FYI so not totally sure if my thinking is correct here. Maybe I should measure my own humbucker output voltage (I will) and maybe I can get it around/under .5 volts rms by lowering the pickups. We’ll see. Please comment if you can. Thanks!

Bob Goodman

Same here continued...

Oh I was supposed to link a video in the previous comment, oh well. I did it myself. I tested the output voltage of my guitars using a multimeter and my guitar cable. My les paul went up to 1 volt rms. It was probably .7 Vrms on its own. When I turned on my boss ns-2 noise suppressor it shot up like .2 V. My tone press compressor also increased the voltage as did the Strymon reverb and delay. So there you have it. I think this is the answer for me at least. I just set my source audio eq pedal to lower the volume of my les paul at full chord strum on the neck pickup to under .5 Vrms and set it as one of my favorites. My amp has been cured! I was worried I had to take it back to a tech but all seems well.

Here is that link I was referring to where the guy measures the output voltage of his guitars: https://youtu.be/SkQsXAvDnwU

Hope this helps with your issue greatlakesurf. Please let me know.
- Bob


Interesting suggestion

Howdy Bob,

I ended up bringing my amp to a tech who re-soldered the connections on the main board, looked it over for any other issues, and found that one of the wires from the power transformer was soldered to the wrong place on the main board.

My amp has been working pretty flawlessly the last few months. HOWEVER -- I've noticed that when I have the bright switch on, I get the same noise you describe. I love playing with the bright switch on, but the tech who serviced my amp warned that it lets pretty much all the frequencies through. Bright switch off, no problems.

I play with a Jazzmaster, lots of reverb, a little drive sometimes, and I like to get heavy and loud with lots of fuzz. I'll look into measuring the output of my guitar to see if it's too much for what the amp is rated for... Cool suggestion and thanks for sharing that info from the service manual of the HD-130!

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