ShortScale.org

Couple of questions for yous:

So I ended up buying that Harmony H306 that I posted about, (and got no replies ) a while ago.
Right from the getgo, the seller informed me that there was an undiagnosed issue which was causing a slight but constant buzzing and eventual low range fart-out, at high volume. I went ahead with it thinking I could probably resolve the issue myself. So after changing out the 50 odd year old preamp and rectifier tubes (the power tubes look ok), the sound definition has somewhat improved but the buzzing and farting remains. I don't know how to expess this technically but the sound seems mechanical in nature. It doesn't sound like an interference/faulty circuit kind of thing, if that makes any sense.

So anyway, first question:
Am I misguided in suspecting that the driver (original Jensen) to be the culprit?
Despite it's age, it looks pretty much intact and doesn't show any obvious signs of damage. Could it simply have dried out?


Secondly, if the speaker turns out to be fine, what do you think is most likely the problem with the amp. Could a bad capacitor cause this kind of behavior?

And lastly, assuming that it IS a speaker issue, what would be your recommendations regarding a good, budget oriented 12 inch speaker? (trying to keep it under 50w.)

Any input in this matter will be greatly appreciated. (unless you choose to tell me to FUAC OAFF, N00B, in which case FUAGK YOU TOO.)

A constant buzzing, even when not playing, makes me think filter caps. It would cause low-range fart as well since the amp would have trouble drawing the power it needs for low frequencies. I'd replace the filter caps first and see where you stand afterwords.

There also may be a voice-coil rub or misshapen cone problem with the speaker. If you want a new speaker cheap, look at the Weber Sig series. I have the Alnico 12 and it rules once it's broken in.

The constant buzzing definitely sounds like a degradation of the filter caps, though.

Thanks for your help Duo.

This reminds me of two things that I forgot to bring up.

The issue is not present unless the amp is passing a signal.
However, no matter how minute the signal, the buzzing will be present.

something I failed to mention is that there is a non functional vibrato circuit
which is driven by a weird metal sheated tube (6sh7). The tube, itself looks
like it's new and opening up the vibrato pots does not inject any noise into
the signal. I haven't had the chance to check the actual circuit to see if it's
been bypassed and I have not tried running the amp without the tube to see if
this interrupts the circuit but I will.

AHHHHH - if it's only when passing a signal, it's more likely to be a speaker problem. With bad caps you would get constant noise, even idling.

Do you have a footswitch for the trem? The switching shown in the schematic would turn off the trem with no footswitch connected.

I assume you found this schematic:
http://www.freeinfosociety.com/electron ... nyH306.jpg

A speaker can look fine and still have problems. www.tedweber.com has some articles about diagnosing voice coil rub and misshapen baskets. It might help you figure out if it's a speaker issue.

Yes I've seen the schematic but I don't have the skills to interpret it.
I'm relieved at the thought of this likely NOT being related to a bad cap cause, like many, I'm absolutely terrified by the idea of discharging it.
Alot of people make it sound like disarming a freaking bomb. I know I'll have to cross that bridge, eventually, though...

Any thoughts on the Jensen MOD series and the Celestion rocket 50?

Discharging a cap is no big deal - like anything dangerous, you take yr time and follow the procedure. I need to dig out the how-to video I had and post it here.

Anyhoo, the Jensen MOD series is very good for the price. I haven't heard the Celestian, but I can't imagine they'd make a bad speaker. I tend to pump Weber stuff all the time cause $45 for a 12" Alnico is crazy cheap, and it's actually pretty good.

I'm going to check out those weber anico 12's for sure.
I think one of my local shops actually sources them, too.

Oh, and thanks for the link. I haven't gotten to the articles you mention, yet but I see the website carries alot of speaker related products that may come in handy.

So I went ahead and got me a Weber Alnico 12 and since it was uber cheap, I picked up an Eminence Texas Heat as a spare and in the spirit of variety. (I'm a Jensen Man.) I fitted the amp with the Weber and well, for one thing, PROBLEM SOLVED. That became apparent as soon as I took the old speaker out, actually. one of the mounting holes on the basket had developed a crack almost half of the way across one of the struts. I was able to flex the crack by putting a little pressure on the outer edge of the spearker, so I think it's resonable to think that that was the source of the buzz.

But anyway, good call on the Weber, man. I love that thing. It sounded wonderful right out of the box and I can only imagine how good it's gonna sound, once I put it trough it's paces... It completely transformed the voice of that amp, too. I got alot of dormant clarity shaken up, Now it sounds very close to a blackfaced Champ, only with more complex low end and considerably more power.

Thanks for the advice.

Glad you dig it. Those Weber 12s are basically Jensen clones, so they're a good match for the old American-voiced amps. Mine got a bit softer, a lot fuller, and louder after some play time - there's more good stuff on the way!

laterallateral wrote:I'm going to check out those weber anico 12's for sure.
I think one of my local shops actually sources them, too.

Oh, and thanks for the link. I haven't gotten to the articles you mention, yet but I see the website carries alot of speaker related products that may come in handy.

Which store has the Weber's for sale in town?

I've been wanting to replace the craptacular stock speaker in my Pro Junior with something good.