If you were going to have someone build an amp for you to use with an existing cab what would one specify beyond tube compliment when commissioning the project to someone who probably doesn't have experience with harp amps as such but is nonetheless a qualified and experienced amp tech?
It would depend on the size of the cab, the cost involved and the requirements needed. As a rough guide though if it was a small cab, then I'd go for a Fender 5F2 circuit. A mid sized cab, a Fender Princeton Reverb circuit. A large cab then either a Fender Bandmaster or Bassman circuit. Then I'd have the circuit tweaked to make it more harp friendly.
I'd recommend that whatever you go for, make sure he uses CTS audio volume pots, rather than Alphas...the Alphas feel nice but even the audio pots can have a bizarrely fast ramp up & can be harder to dial in.
If the amp is fixed bias, make sure that the bias adjust pot has a sufficient range of adjustment to dial in the tubes from say 6-35mA (if we're talking 6L6/5881/EL34), that may be from -65dc on the grids up to -75vdc for a high voltage amp (470-510vdc). With bassman & early brown amp (Concert/Bandmaster/Pro) bias circuits this is easier if the pot goes in place of the 10K-15K dropping resistor (put a small value, fixed resistor in series), not the 56K load resistor.
If cathode biased, have a switch to take out the power tube cathode bypass cap, having it in will give more gain, maybe a switch to ground out the out-of-phase power tube grid too (NOT FOR FIXED BIAS)...then you can have 3 modes of operation/break up levels with the cap in/out & grid grounded/not.
If you are replicating an old design that you have heard, get some feedback on actual voltages (power tubes especially) in that amp as it is played today, rather than try and achieve voltages seen on old schematics.
Don't try and cram a complicated circuit into too small a space.
Go for bigger W rated plate resistors if you fancy doing low gain preamp tube subs - 1W minimum, 2W would be nice, carbon film or carbon comp.
Use shielded wire for the grids (wires from inputs & vol pots), use screen grid resistors (whether shown on old schem or not) & grid stoppers (1.5K -2.2K).
If possible might be nice to have each stage in the circuit driven by it's own preamp tube, so you can change the gain of one stage at a time (already the case with a tweed bassman, more for tolex Fender style amps, could be done for single preamp tube amps too).
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Last Edited by 5F6H on Jun 10, 2013 4:27 AM
Thank you Mark. I'll print that out 'cause it's Greek to me. To clarify, I'd be looking for something like a 20 watt amp, 2 x 6v6s, with a 1 x10" combo cabinet.
I have an Avenger, a Zoo 2, and I just picked up an HG2. The HG2 I bought non- working at a price. Apparently it keeps blowing fuses. I rolled the dice on it in the hope it's an easy fix like perhaps just changing tubes. In any event, I have tools for large and really small gigs/recording but would like something in the box that's in between. I bought something that I thought would suit but that is not going to work out so I'm left with a combo cab, a speaker, and a few amp parts. ---------- LSC ---------- LSC
LSC, it sounds like your HG2 may have a bad power tube.
I like the advice from 5F6H. Also check out this article from Gerald Weber: Harp Amp Secrets I'm not sure I'd trust the build and tweaks to a tech who has no blues harp amp experience, though...
If you are looking for a 2x6v6 harp amp with one 10-inch speaker you might consider the new Mission Delta Sonic that will be released in the next couple weeks: $899.
I'm in love with my latest built amp. A Harp modified Blackface-ish normal channel 6V6 amp. It is a lot of small things who made it good. Such as a mid-pot instead of a resistor, a 6G5a tonecontrol, a presence control as it built in a bassman RI. And as Mark says. CTS pot's as volume pots. The differenc between Alpha and CTS is huge.
Edit. This is a clip. I hate to play without backtrck..... http://www.youtube.com/watch?v=PGv60QXHYnc
Last Edited by arnenym on Jun 10, 2013 12:15 PM
A duff power tube on the HG2 is what I'm hoping. I have some NOS RCA tubes to swap. I just need to pop out and get some fuses before I start the experiment.
I'll check out the Gerald Weber site. Amp techs who are familiar with harmonica players requirements are pretty thin on the ground. I only know one in this town but he's moving out of state soon. The guy I'm going to ask about it may or may not have the knowledge. I'm in no rush. Just something I'm looking into.
As to a Mission, I'm looking to salvage what I have in hand not buy anything new, especially in that price range. Besides, I will not do business with Bruce Collins. I know some people like his amps and he's a friend of yours but I have my reasons. ---------- LSC ---------- LSC
Rick - I don't think an open forum is really a place to discuss someones personal reasons for not wanting to do business with someone. That would be better discussed via personal email, as it could be a highly private matter. That is presuming that LSC wishes to discuss the matter at all. Just my opinion.
Just to make sure I'm on the same page here with you....these are two completely different projects you're talking about here right? The HG2 and the potential new amp build?
On the spare parts you say you have laying around, what kind of speaker and cabinet do you have to work with? ----------
Hawkeye Kane
Last Edited by HawkeyeKane on Jun 10, 2013 1:07 PM
@ Rick - As KIngsly said, I don't think this is the place to discuss it. My beef is my beef. However if you would like to send me an email off post I have no problem telling you.
And yes, as I hoped the HG2 blowing fuses was simply a matter of swapping out the power tube. I popped in a new fuse, replaced the Russian E-H 6v6 with an NOS RCA and replaced the GT pre-amp tube with another RCA just for good measure. Turned it on, waited a little while, then plugged in a mic and had a blast. No problem. It's been sitting for about half an hour now and is still just fine.
@Hawkeye - Yes it's two different amps. The HG2 is sorted now. The other has a 10" Kendrix ceramic and the cab is maybe half again larger than a Champ. ---------- LSC ---------- LSC
Last Edited by LSC on Jun 10, 2013 1:58 PM
Gotcha. I kinda thought that was the synopsis, but I just wanted to be sure I was clear.
Have you thought about perhaps building a reproduction of one of the old Gibson or Valco circuits into it? Just for something a little different? ----------
Hawkeye Kane
Last Edited by HawkeyeKane on Jun 10, 2013 2:38 PM
I just wanted to follow up a bit on LSC's issue with Bruce Collins at Mission Amps. I got a couple of emails from people wondering about it. While I can't divulge the details, I can tell you that LSC has never ordered or owned a Mission Harp Amp. As far as I know he has never played one. Bruce did not rip him off or anything like that. It was not a dispute over the amp's price or quality or performance. In fact, it was not a dispute at all. It was just LSC's opinion, to which he is entitled, and which he felt compelled to share here without elaboration.
One cool thing... LSC and I discovered we have a mutual friend, an ex-pat Brit blues player who has lived in Denver for a couple decades now. LSC toured Europe with him back in the day.
To return to the original question, I'm thinking perhaps something on the lines of a Masco ME17. Where could I find a schematic and what would be worthwhile modifications to that basic design? Not interested in a lot of bells, whistles, switches, or dancing girls.....well okay maybe some dancing girls. ---------- LSC
If it's a Masco you want, I'd hit up Skip Simmons. Let's face it, he could very well be considered the Masco Master. He's bound to have a schematic for you. Probably some of his own ideas for harp-friendly mods too. ----------
Hawkeye Kane
Last Edited by HawkeyeKane on Jun 12, 2013 9:19 AM
Keep in mind the Masco uses tubes that are much harder to find these days. They're still out there, but it ain't like 12A*7's plus 6V6's... ---------- ---------- /Greg
One of the features of the Masco amps that was used in the Mission 32-20 amp was the paraphase inverter. It gives the amp a nice soft colorful crunch.
But it took hours of trial and error to get just that little part of it right. Having been through a few amp projects that went from concept through design and build, I would recommend against doing it, unless you have Mark Burness or somebody like him doing the work.
So here's where I'm at for the moment and once again would like to ask for advise. Seems like the more I know the less I know. I usually solve these things by trial and error but I figure a lot of you guys have already gone through that process.
Just to remind, the goal was to get something with more volume than the Zoo or HG2 but not as large as the Avenger or Super Cruncher and not a big sum of money.
I've had a couple of email exchanges with Skip Simmons who tells me that it is unlikely an amp with circa 20 watts is still not going to get me very far using just a single 10" speaker. He suggests just selling off the chassis and using the cab as an extension. He could build me an amp but it would be a bit beyond what I'd like to spend. In light of his comments about the speaker I'm not sure if it would give me what I need anyway.
Now then, I've got the HG2 and I was wondering what, if any, increase in volume might be available by adding an extension cab and, if that is a possible, option how one would go about rewiring the cab. BTW, the cab conveniently has an output jack on the back of the cab for an extension speaker and the two together looks well cool, though that is not any sort of priority. ---------- LSC ---------- LSC
Well, usually when you rewire an amp to have an extension circuit, it cuts some of the output to the internal speaker, and also won't have as much as you can possibly get going to the extension either. One thing I like to do is run two amps together by way of a line out. Is your Zoo Heumannized, LSC? ----------
If you use a decent 10" with a 15-20W circuit, you can get significantly louder than a single-ended amp. Pro Jr, Princeton, Laney LC15, Wezo ME18 (OK a bit more W) all spring to mind.
The HG2 with more speakers may get a little louder, but will still only be as loud as a single ended amp with more speakers. If you want to go that route though, I'd replace the HG2 speaker with one of twice the ohms rating and add a speaker of the same ohms to the ext cab, then wire the 2 cabs in parallel. When you use the HG2 with just it's own speaker you will have a little mismatch, but you're expecting less volume in this mode anyway.
The other cab has a working chassis in it already? If it functions, without necessarily being ideal, there is probably some room to move to make that a better proposition? I mean you started with an “unknown quantity”, looked to have another “unknown quantity” built to replace it (even if you largely copied another circuit, you would still end up with differences), why not cut out the middle man & see if you can improve the original amp. As a functioning chassis, with no cab, I don’t see it fetching a great resale, so you wouldn’t seem to have a lot to lose?
If it doesn’t pan out & you decide you don’t want the hassle, you can still take up Skip on his build offer.
@HawkeyeKane - The two Zoos I sold were both "Heumannized" though not by Greg. The Zoo 2 I kept is dead stock except for the power cord. I once strung three Zoos together which looked way cool but wasn't significantly louder than just the one.
@56H - What was explained to me is that the current chassis has design flaws which make it impractical to ever turn into a proper pro grade amp. It was built as a private joke and never meant to be released into the wild but it escaped.
I'm becoming persuaded to go with,ideally, the original plan of having someone build a chassis that will fit into the existing cab or, plan B, going the separates route.
I'm quite tempted to commission Skip. I know he's pricey but I'm selling off some mics and such to trade for getting exactly what I want with as little compromise as possible. The last couple of years I've been able to go that route and have been finding myself finally ending my seemingly never ending search for "What I'd like really is...."
The very best amp I ever played through was a Masco MA-25 with the two original 12" cabs. Redefined the term "huge sound" but was impractical for gigging. I sold it at a time of financial struggle - like I ever have a time without financial struggle - the pain of which was mitigated by having made a pretty substantial profit on the deal. ---------- LSC ---------- LSC
"I once strung three Zoos together which looked way cool but wasn't significantly louder than just the one."
You might get a different result with a different amp strung in. Give a try to the HG2 into the 'Zoo. Dink around with the volume and tone. I bet you'll find some interesting results.
LSC, Skip is right if what you are looking for is loud gigging levels. But 15-20 watts with 1x10 can get loud enough for most performance settings, and if you include a line out you are covered.
But I am not understanding something: If you already own a Cruncher and Avenger why would you be concerned that the new project would not be loud enough? You already have loud covered. And it would certainly be louder than either of your two small amps.
Mark, Wezo claims 30 watts for his ME-18 amp, so it is in a different class. I have played the amp and it is very very good, nice big ripping tone and loud. But rather expensive.
LSC, I think a fixed bias 2x6V6 18-watt 1x10 amp would fill your need nicely.
That's just it, I sold the Cruncher to buy the Avenger. So yeah,I've got two pistols and a cannon. I just need the rifle. I think a 2x6v6 would fit into this cabinet a treat but as you say finding a harp friendly builder can be problematic.
I tried my non-reverb deluxe today which is 2x6v6. I just plugged and played. I could hear some potential but with the 12ax7 the gain was, well you know. And of course it's a 12" speaker. I'll try swapping the tube later and see what that gets me so I at least have some point of reference. I wish had had a couple of the PA heads I had to sell off a few years ago. There were some would have been perfect and could have easily been adapted.
Actually there's a very clean Bogen HE10 on Ebay right now. ---------- LSC
Last Edited by LSC on Jun 14, 2013 4:49 PM
