Harmony H305 Schematic needed

[joe.dollar]

Would anyone happen to have a schematic for an old (1960) Harmony H305 handy? I recently got the amp essentially for free, and didn't think much about it. Just for the heck of it, I did a little reading on the web about the amp and it sounds like people really love these amps.

I plugged mine in and it works, but it's very noisy. Just wondered about recapping etc.

Anybody care to offer opinions on wether or not new resistors (metal film) could/should be installed just to ensure everything's up to spec? The amp has the old carbon resistors that are pretty much original looking. A few things seem to have been worked on "under the hood" of this amp, but I just thought a schematic would be nice to look at all the same.

Any help is GREATLY appreciated!

[pdf64]

The free information society kindly put up the schematic from my H306, see
http://www.freeinfosociety.com/elect...ew.php?id=2287
which might give you a general idea about the type of circuit designs they were using then ie grid leak bias on the pre amp. Before you go replacing lots of perfectly good resistors, try to fault find which stage in the signal chain the noise is coming from, and just change the bad one. Most likely a plate resistor in the pre amp, or something else with lots of dc. Assuming you've swapped in known good tubes?
Hope that helps - Peter

[joe.dollar]

I shall look that schematic over! Thanks for your opinion regarding replacing resisitors etc. I have an Ampeg Rocket that has lots of carboncomp resistors and the phantom noise problems were very bad. When the amp was first turned on and "cold" it was fine, but as the various components warmed up, things got noisy. Apparently the carbon-type resistors are a little more prone to heat affecting their operation. BUT, I agree. I shouldn't be replacing perfectly fine compnents that still have lots of life left in them.

[Enzo]

Schematic Heaven doesn't list the 305, but it has lots of other Harmony models. You might see if any match your amp with minor changes.

[joe.dollar]

I was looking at the schem for the H306, and it's pretty similar. I think I can get a few ideas from that amp that apply to my 305.

[Andrew M]

If it is that the one with 2 12ax7s, 2 6v6s and a 5y3 rectifier, then I had one of those. I rebuilt mine as a Fender tweed (5E3) and it sounds so much better. A friend of mine who didn't know I had rebuilt it was baffled as to why my little amp sounded so good all of a sudden.

Andrew.

[joe.dollar]

Hey Andrew. Thanks for the post. I was hoping to hear from someone who'd done some mods to one of these. Your mod has definitely got me thinking.

Mine is definitely the same as yours tube-wise. Mine has only 3 inputs (2 on channel 1 and 1 on channel 2) , not 4 like some schematics show.

As i had posted previously, mine is pretty noisy, not very loud and it seems mostly original. The cabinet is pretty bad, and being always at the ready with my dovetail/ fingerjoint jig, I'm going to do a new cabinet that's a little bigger and not made of pressboard. I was thinking about re-capping, possibly re-doing resistors, and then running it through an old 15 inch alnico that I have.

Did your mod give you a substantial volume boost?

[Andrew M]

It was a bit louder, and seemed more dynamic (touch responsive). It does the chimey Fender thing (clean with just a bit of dirt) when strumming chords and distorts nicely when you pick harder. Also I have an old Ibanez Sonic Distortion which pairs really well with it, makes a great lead tone at a reasonable volume.

Andrew.