# Harmony 305C troubleshooting help



## nbs2005 (Mar 21, 2018)

Hi all,

I fired up this amp yesterday and got some horrible noise after about 10-15 min of of use. It is now doing this every time at start up after a few seconds. Steps to reproduce: amp with single guitar plugged in (no pedals), channel 1 and 2 jumpered. Turn the amp on, sounds fine for 5-10 seconds then jumps to a very loud hum. I tried it 3 times in a row with the same results. 

The amp is a '62 5e3 clone. It's been extensively re-worked and has worked flawlessly for me for the 2 years I've owned it. I was going to get some tubes to start swapping to see if it's something simple. Any other troubleshooting hints? 

Thanks,
Jeff


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## Frenchy99 (Oct 15, 2016)

Nice rebuild !

I`m a novice in amp repairs but if major hum after warm up, I would verify the caps first. I know you have all recent caps in there but the IC caps are known to go bad and leak.

Following this.


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## greco (Jul 15, 2007)

I'm sure it is related to the angle of the pic and not wanting to sound critical of your amp in any way, but there are a lot of unprotected component leads that don't seem all that far apart.

Maybe some leads are touching?
I guess this is extremely unlikely as the amp has been fine for 2 years









Following with interest.


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## Paul Running (Apr 12, 2020)

I agree with greco...there is a high risk of shorting there...it will follow Murphy's law. When you strip 18 or 16 gauge wire...save the strippings for component sleeves to insulate the leads...reduce chances to shorts.
I do all point to point wiring...it don't look pretty however, when wiring this close, I make sure to insulate well:


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## Paul Running (Apr 12, 2020)

If it's power supply hum and you have a DVM, you could monitor the B+...on DCV, the meter will fluctuate and on AC you will measure the hum voltage...if it's a loud hum you may measure over 100VAC at 120Hz. 100VAC modulating the OPTFM will measure about 3 to 5VAC on the output of the amp...about 3W of audio at the speaker...loud.


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## nonreverb (Sep 19, 2006)

I agree with the above posters that insulation is a must where components...especially ones carrying high voltage are concerned. That said, I don't believe that's the problem. My first guess is you might have a bad tube that's failing once the heater is getting to full power. You might try pulling each tube starting from the first preamp tube to see if it changes the symptom.


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## butterknucket (Feb 5, 2006)

I'm not a tech, but it sounds like a capacitor issue to me.


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## Frenchy99 (Oct 15, 2016)

nonreverb said:


> I agree with the above posters that insulation is a must where components...especially ones carrying high voltage are concerned. That said, I don't believe that's the problem. My first guess is you might have a bad tube that's failing once the heater is getting to full power. You might try pulling each tube starting from the first preamp tube to see if it changes the symptom.



Good one! 

I would check tubes automatically on any amps but have the habit of doing so since I have a tube tester. Not ever one has.


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## nonreverb (Sep 19, 2006)

Frenchy99 said:


> Good one!
> 
> I would check tubes automatically on any amps but have the habit of doing so since I have a tube tester. Not ever one has.


Eliminate the obvious and easiest stuff first.


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## Paul Running (Apr 12, 2020)

Yes, capacitor quality has improved and tube quality has diminished over time.


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## jb welder (Sep 14, 2010)

nonreverb said:


> Eliminate the obvious and easiest stuff first.



One of the first things I do in similar scenarios is wiggle all the tubes around in their sockets and see if it has any affect on the symptoms. Sometimes a little oxidization can cause all kinds of mayhem and is pretty easy to fix.


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## loudtubeamps (Feb 2, 2012)

After the suggested tube swap ,if the noise persists I would at least discharge and pull a lead from the filter caps ,check them with a cap checker and visually.
Look for a minute amount of brown powder around the positive lead where it exits the seal.
I just replaced filters in a Blues Junior yesterday, the ailment.....high pitched oscillating in the first stage...sounded like a bad lead dress and varied with changes in volume or tone controls.
I have in the past year or so , worked on 3 of the smaller Fender amps using these iC caps, all had failed....garbage IMO.


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## Lincoln (Jun 2, 2008)

Frenchy99 said:


> Good one!
> 
> I would check tubes automatically on any amps but have the habit of doing so since I have a tube tester. Not ever one has.


I don't have a tube tester


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## Paul Running (Apr 12, 2020)

Lincoln said:


> I don't have a tube tester


Unless you are selling tubes, it's an expensive investment for a HQ set...in-circuit testing should provide enough intel.


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## nbs2005 (Mar 21, 2018)

Thanks all for the prompt replies. I will, in order, wiggle/re-insert the tubes, then swap tubes from my other amp to test. If the problem still exists, it's off to a tech as I didn't do the work on this and don't have the skills to do that.


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## greco (Jul 15, 2007)

Good Luck with it! 
Please update us when you have any new information. Thanks.
Interesting thread!


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## nonreverb (Sep 19, 2006)

loudtubeamps said:


> After the suggested tube swap ,if the noise persists I would at least discharge , pull a lead from the filter caps and check them with a cap checker and visually.
> Look for a minute amount of brown powder around the positive lead where it exits the seal.
> I just replaced filters in a Blues Junior yesterday, the ailment.....high pitched oscillating in the first stage...sounded like a bad lead dress and varied with changes in volume or tone controls.
> I have in the past year or so , worked on 3 of the smaller Fender amps using these iC caps, all had failed....garbage IMO.
> View attachment 347603


Indeed Doug....They've had problems with those and the blue Lelon caps as well. The Lelons usually all have to be replaced.


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## Frenchy99 (Oct 15, 2016)

Lincoln said:


> I don't have a tube tester


I`m surprised you never picked one up along the way with the amount of amps you build. Some are not expensive on the used market.


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## Lincoln (Jun 2, 2008)

Frenchy99 said:


> I`m surprised you never picked one up along the way with the amount of amps you build. Some are not expensive on the used market.


It's sure not for lack of trying. I've had several deals on one slip through my fingers. I am not as lucky as you are. 

I don't use any used tubes, and so everything is new. I have enough to worry about without throwing untested tubes into the mix.


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## loudtubeamps (Feb 2, 2012)

Frenchy99 said:


> I`m surprised you never picked one up along the way with the amount of amps you build. Some are not expensive on the used market.


I don’t use a tester either, I had a couple of basic units years ago.....now I use one of my amps.
Once you have a piece of “test equipment “ you are familiar with, the real world tester (amplifier) seems to me a more logical and definitive approach.

I know what the plate voltages (for a given tube) should be , within reason and I can measure those voltages along with the output signal (given a measured input signal) and most importantly, I can hear what the tube is doing.
Admittedly , I’ve never had the opportunity to use an elaborate tester and I can only guess as to it’s diagnostic capabilities.


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## loudtubeamps (Feb 2, 2012)

Paul Running said:


> Unless you are selling tubes, it's an expensive investment for a HQ set...in-circuit testing should provide enough intel.


Exactly!👍


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## nbs2005 (Mar 21, 2018)

Here's where I come back and sheepishly explain what I've found out. 

Basically, I forgot the second of the two most important troubleshooting steps (the first being is it plugged in); are all the cables in good nick? Well it turns out the answer is no, they are not all in good nick. I've had my second guitar cable failure in 6 months. This was discovered when I tried to play a second amp and had nearly the same issue. Trying the one last long cable I have, everything works as it should.

Thanks for all the help and learn from my mistakes; check the damn cables.

Cheers,

Jeff


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## Frenchy99 (Oct 15, 2016)

Here I was going to offer you $20 for you're non working amp ! 

Congrats on the fix, new cable !!!


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## greco (Jul 15, 2007)

nbs2005 said:


> check the damn cables.


Not wishing to embarrass you or rub it in, but...
(next time)*CHECK THE DAMN CABLES *(FIRST!)


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## Frenchy99 (Oct 15, 2016)

greco said:


> Not wishing to embarrass you or rub it in, but...
> (next time)*CHECK THE DAMN CABLES *(FIRST!)


Lol... I think I got a Traynor YVC-50 for $100 from the same problem !


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## Paul Running (Apr 12, 2020)

I used to use the line: *Loose nut in front of the amp?* People will look at you...what?


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