Harmony H304-A Troubles

[Megatron]

Hello All...new to the forum and in need of expertise!! I am currently restoring my old harmony amp that smoked a power transformer years ago. The closest fit I could find was a Champ transformer, so I installed that and a new output transformer. I also recapped the beast and installed new wiring to replace the brittle old stuff. I have a few problems, the main one is that I get very low output even with the volume pot all the way up and it is really fuzzy/distorted. Tried different speaker, etc. I found and fixed a few problems, ie cathode caps installed backwards(yeah, I did that) and miswired B+ at filter cap(went from 3 lug to 4 lug cap can). I emailed ClassicTone and they suggested switching the leads on either the OT primary or secondary...so I will try that soon. Also, I am curious about the B+ voltage (about 430VDC)...I wonder what the B+ voltage was on the original Harmony PT?? Reason being is that the bias resistor is 250ohm whereas the Champ is 470ohm...any ideas/suggestions??

Thanks!

[sgelectric]

Welcome to the forum.
There are many skilled technicians here who will help you sort out your amp.It is useful to post a schematic and possibly pictures to help with this process.


Schematic for Harmony H304-A

http://www.webphix.com/schematic%20h...mony_h304a.pdf

[Jazz P Bass]

The B+ on the Harmony was certainly less that 400Vdc.
All of the filter caps are 400WVdc.
I would think that Harmony would not exceed the rating.

[Megatron]

The B+ on the Harmony was certainly less that 400Vdc.
All of the filter caps are 400WVdc.
I would think that Harmony would not exceed the rating.

Thats kinda what I figured...guess I'll have to use the zener diodes to drop voltage from the PT? I've got a couple of schematics, but nothing indicating voltages.

[Megatron]

Welcome to the forum.
There are many skilled technicians here who will help you sort out your amp.It is useful to post a schematic and possibly pictures to help with this process.


Schematic for Harmony H304-A

http://www.webphix.com/schematic%20h...mony_h304a.pdf

Thanks a bunch! I will try & post some pics tonight if I get a chance...

[Megatron]

[dkevin]

Harmony H304A voltages

I recently acquired a Harmony H304A amp . I also have an older 304 that I had been working on and on and on...but never was quite satisfied with it. The 304A I hoped would help me solve some of the issues I had with the earlier amp.
Anyway, the 304A operating voltages with all the components verified and replaced as required were, V1 cathode tied to ground...V1 plate=25vdc...V2 cathode=2.84vdc...V2 plate=202vdc....V3 cathode=13.6vdc...V3 plate=284vdc...V3 screen=281vdc. The supply voltage from the 5Y3 output is 300vdc.
I hope that these numbers prove helpful to you. The amp sounds great and I am beginning to work on the older version.

[Megatron]

Thanks! I was wondering about that...my 304a sounded real nice when it was working! Do you have any gut shots of the 304a? I'm pretty sure mine was repaired at some point with whatever the tech had on hand. Now I have a Champ transformer because that's the closest I could find. Problem is, now I'm about 100V over where I should be, according to your numbers. What should I do? Thanks a bunch man!!

[davohilts]

I've got a 304A that i'm about to do some work on. Don't know if it is original, looks like some newer caps were put into it. It has a 40-20-20 450 volt cap can so the 20mfd x 4 shown on the schematic must have 2 caps tied in parallel for 40mfd on the b+ tap. Here are a couple of gut shots of the amp. Hope this helps.

[Megatron]

Original pics of mine...now I'm even more confused??? I just found that I only have 3.1vac on one leg of the heater circuit...bad brand new PT? I'm gonna try to cut the center tap and make an artificial one with 2 100ohm resistors and see what happens....thanks for the pics!!

[davohilts]

Hey Megatron,
I have been working on my amp and had a couple of questions about the circuit as it is something I've never seen as of yet. On this link I got some modification advice that I'd like to pass on to you. Read all the posts and it might help you with your troubles.
Harmony H304A Circuit question

and this one for the comparison to the univox amp

http://music-electronics-forum.com/t8864/
Dave

[Megatron]

Finally got it working, sounds great!! I installed a zener diode on the center tap of the secondaries to drop B+. I still had problems with the heater voltage, so I isolated the heater windings and discovered that I got 6.8V across the windings(no tubes installed)without the center tap grounded. Then I realized that the H304A in its original configuration has one leg of the heaters grounded...so I was creating a sort of short circuit by grounding the center tap. Hence, very low output and very hot PT!! Live and learn, right?
I will try to post a better pic of the finished product and maybe a tone sample...thanks for your help!

[plook]

Megatron, i have exactly the same problems as you on my Harmony H304, very low output and very distorted. i am going nuts trying to fix it. The 6BF6 has been replaced with a 12AX7. I think i have tested every component, caps, resistors, speaker, transformers, valves, filter caps, and yet i can't nail the problem. Can you help?

[davohilts]

The output transformer can be a tough one to test and could be the culprit.

Megatron, i have exactly the same problems as you on my Harmony H304, very low output and very distorted. i am going nuts trying to fix it. The 6BF6 has been replaced with a 12AX7. I think i have tested every component, caps, resistors, speaker, transformers, valves, filter caps, and yet i can't nail the problem. Can you help?

[plook]

I've changed out the OT with two different new ones, but it sounds EXACTLY like a bad OT problem, it's not though.