Amp Tech Thread / Ask a tech Q

[Slow]

Sigh. I'm buying a Musicman HD-130 head thats going to need a recap and retube.

Looks like it's time to get confident.

[Hemisaurus]

Really confident, and you'll need some really good EL34's. 725V on the plate means much owchie

[VOLVO)))]

6CA7's were standard, originally, in the earlier ones, eh?

[Hemisaurus]

Pasted from Eurotubes:

E34L

Factory description: Gold plated control grid for improved fidelity. Special plate alloy improves plate dissipation as compared to the standard EL34 resulting in stable performance at higher power levels.

Our observation: This tube has about 20% more head room than the standard EL34 and it also has a deeper, tighter low end. The E34L is also a bit punchier and more aggressive than the standard EL34 which makes it a Great tube for Matchless, Bogner, Carvin, Peavey and all Marshall amps. I have them in one of my old SUNN heads. Incredible sound!  The E34L and the JJ KT77 are the only EL34 type tubes that I have found that will stand up to the 700 plus plate volts found in the Musicman HD 130 amps.

[VOLVO)))]

So I should stick KT77's in 'er? That's fine with me...

[Hemisaurus]

So he says, the different impedance would be something I'd think about, but if he's done it.

Mine came with a set o GT 6CA7's and I never had to retube it.

[VOLVO)))]

That's what I'm saying... he sells big bottle 6CA7's, and they're cheaper than the 77's, and they're the tubes that should be in that amp...

[Hemisaurus]

So use the E34L? The above said E34L or KT77, and the E34L is cheaper than the KT or the 6CA7.

[Hemisaurus]

and in answer to your original question, no, they spec'd EL34 or 6CA7's for that, back in the day when men were men, and tubes were tubes 

[liquidsmoke]

I tune down to A and play a lot of heavy doomy chugging type riffs into my Laney GH50 with the gain all the way up into a 2x12 cab that has Eminence Governor 75 watt speakers. When I turn the amp way up(like way louder than practice volume) the speakers distort a great deal. If I was to swap the Governors for some higher wattage speakers, say in the neighborhood of 125 or 150 watts would I be able to turn up really loud without getting a lot of speaker distortion? How bad is speaker distortion for speakers? How do you tell whether you are hearing speaker distortion or tube distortion? The thing is that with my old 4x12 with Eminence Manowar 125 watt speakers there wasn't any excessive distortion at super loud volumes, just super super loud sound. I got the 2x12 because I wanted a lighter cab and I also wanted something with some warmer/darker sounding speakers, Manowars are pretty bright sounding. I don't think Eminence makes any higher wattage handling 12" speakers that aren't bright, I'm not sure who does.

Right now I don't really need speakers that can handle my amp on 7 or 8, we haven't started playing out live yet and even when we do I'm not sure how often we would want that kind of volume but I'd like to be able to do it and do it right if it's needed. But if that sounds crazy please tell me so. I've never been in a band that actually gigged and have no idea what it's like to be running through a PA and have stage monitors running various signals and what not.

edit: I'm thinking that some 15" Big Bens would probably do the trick but I really don't even have money for new speakers let alone a new cab or 2 new cabs.

[Hemisaurus]

This is definitely one of those wish it was here moments. Speakers can distort in a lot of ways, but unfortunately so can speaker cabinets. Baffles can rattle, jack panels can buzz, speakers can be loosely mounted, even handles can rattle.

Have someone play your guitar, or feed a walkman or ipod into the fx loop of your amp, and get it to distort, and try feeling your way round the amp, does pressing on anything cure the distortion? Try the joints, the handles, the jack panel, the rear panels, front panels, and check the screws holding in your speakers are tight. Do they screw into wood or does it use t-nuts, etc.

The obvious answer, if it's not the cab would be to pull 2 speakers from your 4x12 and swap them in, you can use your tone knob if they sound too bright, then you'll have a 250W 2x12 and still handle 300W safely on your 4x12, so tell us about the impedances

[liquidsmoke]

I'll check to make sure the cab and speakers are tight and solid but I've only had the thing a few months. I sold the 4x12 so I don't have those Manowars anymore. I did mess with the tone knobs and what not but it seems like a bright speaker is still a bright speaker in the end.

I really don't think a 2x12 can sound as heavy as a 4x12 but you shave 20 lbs with 2 less speakers plus there is usually less wood. That 4x12 was quite wide and a bitch to lug up and down stairs by myself, my shoulders are pretty weak.

[Hemisaurus]

Is the 2x12 closed or open back? Fully closed cabs are going to sound bassier, open back cabs waste bass.

I've heard a Marshall 1x12 sound as heavy as a 4x12, so it's not cab size.

[inductorguitars]

MDF VS Birch ply

It's a trade off. Yes MDF is more dense, but it's heavy as fuck. DUH. Any moisture will degrade it. Eventually it will rot. I have a cabinet in my kitchen that is rotting away from the humidity.

The Birch ply is void free, lighter, and won't rot.

I'm with Sunn use the birch ply.

[liquidsmoke]

Is the 2x12 closed or open back? Fully closed cabs are going to sound bassier, open back cabs waste bass.

I've heard a Marshall 1x12 sound as heavy as a 4x12, so it's not cab size.

I just think 4 speakers sound heavier than 1 or 2, generally. I'm doing pretty well with 2 plus the 15" bass combo for now though.

[Hemisaurus]

MDF VS Birch ply

It's a trade off. Yes MDF is more dense, but it's heavy as fuck. DUH. Any moisture will degrade it. Eventually it will rot. I have a cabinet in my kitchen that is rotting away from the humidity.

The Birch ply is void free, lighter, and won't rot.

I'm with Sunn use the birch ply.

That explains why those cheap-ass MDF cabs I picked up in 1989, and had brought all the way from Scotland by sea are totally not falling apart

Well they're only 22 years old, and on their third set of woofers

[Slow]

MDF VS Birch ply

It's a trade off. Yes MDF is more dense, but it's heavy as fuck. DUH. Any moisture will degrade it. Eventually it will rot. I have a cabinet in my kitchen that is rotting away from the humidity.

The Birch ply is void free, lighter, and won't rot.

I'm with Sunn use the birch ply.

That explains why those cheap-ass MDF cabs I picked up in 1989, and had brought all the way from Scotland by sea are totally not falling apart

Well they're only 22 years old, and on their third set of woofers

Ireland****

[Instant Dan]

Pedal question!

Have a late 90's Deluxe Memory Man reissue with the old 3 prong AC cord. Last night I decided to jam in my bedroom and plugged my Epiphone Valve and DMM into the same outlet and got a loud hum. Even after giving them separate outlets, the hum continued. Went back into the living room and plugged into an outlet and no hum at all, even with the amp and the pedal sharing the same outlet.

What gives?

[Hemisaurus]

Sounds like you have either a bad ground in your bedroom, or something electrically noisy on that circuit.

Get yourself an outlet tester, and check your bedroom, I once rented a place where half the grounds hadn't actually been grounded, which was brought to my attention when I got a shock from my cable box.

[justinhedrick]

Sounds like you have either a bad ground in your bedroom, or something electrically noisy on that circuit.

Get yourself an outlet tester, and check your bedroom, I once rented a place where half the grounds hadn't actually been grounded, which was brought to my attention when I got a shock from my cable box.

i rented a place for a summer that wasn't grounded either. the whole house wasn't. i was always worried about grabbing the door handle of the fridge with wet hands . . . not to mention the ungodly hum from all of my gear. a buddy of mine let me use this outlet box that was ancient that had 2 extension cords that plugged into the outlets, then 4 plugins. but there was a 3rd extension cord that you ran to a rod that he pounded into the ground. worked well, but i was always scared aobut using it.

[Hemisaurus]

Hey Sunn. See the above pictures are actually links.

For some reason the forum is chopping off the last character, or maybe it's this crazy iPad, check it

Yep, it appears to be the crazy iPad

[VOLVO)))]

Yeah, they're fine.

[VOLVO)))]

Alright, opened up my HD-130, to make a list of what I'm going to need in terms of caps. The tubes are solid. You've confirmed that it should be hyper-fuckin' loud. Anyways, I was reading on the MM site that I should replace... every cap in the amp, at this point... What do you say, Herbie? Is that just a load of shit? Also, the big ol' silver can caps, and the slightly smaller but still large blue caps don't have the farad value on them? Does that matter, as long as I replace them with the same MFD/voltage rating... is that the farad rating? Gotta learn somehow...

I know I won't be able to get Mallory replacements, anymore, so where do I source 'em, I tried googling/Mouser, but to no avail because I don't actually know what I'm looking for.

When I do the physical job, is it acceptable to clip the leads from the old caps, and solder the new leads to the old leads, so I don't have to lift the board, or is that half-assing it? I'm trying to save manhandling the boards too much, they're pretty brittle after all those years.

Soon as I get back from the airport, I'll post some pics. I'm having trouble figuring out which is the bias pot, one of them is the trem adjustment, I know that much. The schems online are kind of hard to make out, The chassis number is 2475-130 UL

[VOLVO)))]

Also, if you can find me a printed copy of that Jack Darr book under 60 bucks, ill buy it...


Weber has the caps I need, Axial electrolytic caps?

[VOLVO)))]