Re: [Harp-L] Amp Mods

I've had a G60 for several years. I've actually been asked to turn down. If you monkey with the volume and gain controls I think you'll find you can get a pretty dirty sound without any mods. My experience is that going to lower gain preamp tubes gives you a wider range on the volume control knobs before feedback. That's not a bad thing. It's easier to dial in the sound you want. As has been pointed out, leave the reverb tube alone. I've tried multiple combinations of 12A* tubes. A lot of it depends on how you play and what kind of mic you use. I think you'll find that dynamic and crystal/ceramic mics are very different. Be sure to use the low sensitivity switch setting. Most high impedance mics are hotter than guitars. I have a Weber ceramic magnet speaker in it that I got 6 or 7 years ago. It's a 12F150-O-50w with moderate doping. (Just stumbled across the receipt yesterday when going through a box of electronic junk.) It was the one Ted Weber suggested specifically for harp. I've been happy with it. I also tried an old alnico magnet speaker that originally came from an organ. I got a little uneasy about blowing it out although it sounded good. I think the alnico vs ceramic magnet speaker thing isn't as big a deal as some people make it out to be.

You might consider a high impedance buffer if you have a crystal or ceramic mic. They have a much higher impedance than a dynamic mic. Guitar amps usually have around 100K input impedance. Crystal/ceramic mics like about 5 M. There are kits and circuit diagrams galore on the web. A basic buffer is a very simple circuit. The project box may cost you more than the components.

Steve Ahola on his http://blueguitar.org/ site has some circuit mods for the G40. I really don't know if they are harp friendly or not. He's a nice guy and readily responds to email inquiries.

On 6/22/2013 6:53 AM, Boogieman Peeps wrote: 
Keep the 12AX7 for the reverb.  Start off with a 12AY7 in the first stage
and see what you get.  12AY7 in the other preamp positions is probably
going to get you where you want, but use as few as you can to get there.



On Sat, Jun 22, 2013 at 8:34 AM, MARK BURNESS
<markwjburness@xxxxxxxxxxxxxx>wrote:

Hi Robert,

Can you scan the schematic and post a link to a hosting site?

If it's anything like the G40V it would probably do with a few internal
component changes. The G40V aimed to keep the preamp signal a little
cleaner than a lot of other amps because of the additional gain stage.

In the short term, I'd try a 12AU7 in V1 maybe an 12AY7/12AT7 in V2?



I wouldn't worry too much about avoiding the Chinese tubes, getting the
right balance in tone & response with the preamp valves will depend more on
the gain structure, rather than where those tubes were made. Buy whatever
you can afford/gives you best peace of mind, but no 12AX7 from anywhere
will have the same gain as a 12AU7 from China. I wouldn't worry too much
about changing the power tubes unles you can rebias the amp/get it rebiased
easily locally...bias will be more relevant than tube brand.


________________________________
From: Robert <harmonicaman1968@xxxxxxxxxxx>
To: harp-l@xxxxxxxxxx
Sent: Friday, 21 June 2013, 22:51
Subject: [Harp-L] Amp Mods


I'm wondering if anyone here has ever done any mods on a Pignose G60VR.
It's a 60W tube amp using 2 - 6L6's in the final amp stage and 4 12AX7's
before that. One of the 12AX7's is for the spring reverb. I'm not sure what
each of the other 3 do, besides pre-amp stuff, but I do have a schematic,
and can understand it to some extent.

Eventually, I want to swap out some of the original Chinese parts, like
the tubes and the speaker.

It's got a high-low switch that cuts out half of the first pre-amp tube on
low, and jacks for an effects loop. 4 and 8 ohm outputs for different
speaker combos. One twelve inch speaker in the box.

I'm not up on which tubes would be most advisable, or which speaker. It's
a very clean amp, not much breakup as designed from the factory. For
guitar, it's great. For harp, not as much, yet.



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