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Author Topic: Marshall 3005/Lead 12 Power Trans Question  (Read 15662 times)

Clyde

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Marshall 3005/Lead 12 Power Trans Question
« on: June 16, 2015, 06:41:20 PM »
Looking at replacing a transformer on a Marshall 3005.  Can't find any info on the original tranny.  Only mark on it is 'T4942'.  Per available schematics this matches & breaks down to a 115VAC with a CT 28VAC (14.3 per side...so 28.6) secondary.  Input also indicates 35w & 40VA.

The closest thing I can find as a replacement is from Hammond:  either their p# 166J28, which is a 1A, 28VA unit, or p# 166L28, which is a 2A, 50VA unit.  My 1st inclination is to go with the larger VA rating rather than undercutting.  The smaller rated unit will match for size but there's room enough for the larger. 

Am I thinking this through properly?  Any thoughts would be appreciated.

C

Loudthud

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #1 on: June 16, 2015, 09:45:19 PM »
I'd be tempted to go with the smaller unit. Guitar amps sound better with weaker transformers.

galaxiex

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #2 on: June 17, 2015, 01:23:08 AM »
I'd be tempted to go with the smaller unit. Guitar amps sound better with weaker transformers.

Does that hold for SS amps too?

I was under the impression weaker transformers could cause sag (compression) in tube amps.

Not sure if that is a good thing in a solid state amp?
If it ain’t broke I’ll fix it until it is.

phatt

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #3 on: June 17, 2015, 05:02:35 AM »
A weaker power supply for SS rig won't magically turn sand into glass audio 8)

SS power stage is a very different beast and don't work like a valve Power stage though you can make a Valve amp as tight and correct as the best hifi SS amplifiers with little sag,, Others here will know more.
It's just that Valve powered guitar rigs mostly use the old fashioned basic circuits and came with sag by design.

As to Tranny Q,,, I'd say don't expect a big improvement just by having a bigger transformer.
On the other hand if the transformer failed then a higher VA rating might help.
I'd want to establish why the transformer failed before I made any decision.
My 2 cents, Phil.

Clyde

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #4 on: June 17, 2015, 11:12:17 AM »
Thanks for the comments.  The transformer in question has not failed...just produces a lot of noise that appears to be of a mechanical nature.  Tightening things up hasn't helped but I'm still in the problem identification stage.  Trans is outputting correct voltage.  And I replaced all of the e-caps as what was there was all original & 30 years or so old.

My initial thought was just replace the trans.  Then, trying to find a suitable replacement became more of a search than I expected (i.e. no info on original).  Then it morphed into a matter of principle in finding something that would work.  Not trying to improve the sound necessarily. But then too, it is somewhat of an experiment in seeing how a different trans will affect the overall amp. 

C

J M Fahey

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #5 on: June 18, 2015, 07:24:09 AM »
If the transformer works properly and only problem is mechanical buzz, I wouldn't replace it.

Proper solution is to pull it from the amp (note position of original cables for reassembly) and dunk it in a can of transformer varnish, which is nothing more than glorified synthetic/oil based varnish.
I'd make a braid with wires so as to be able to hang it, upside down, and dunk it in a can of varnish, usual home/furniture finishing type is fine, or so called Marine type.
Submerge just the transformer itself , leave cables outside, mainly to minimize the mess, and let it there for a couple hours, until no bubbles come out and them some extra time, so varnish wets everything inside.
Then you pull it out by the wires (tie some string to them) , let some varnish drop back in the original can and then tie it somewhere so the last drop drips out, put some old newspaper under it.

Leave it at least overnight.

Only difference between household type varnish and "transformer varnish" is that the latter is quick drying, either in an industrial oven or air dry, yours will take at least overnight and will smell like fresh paint (which it is) for a couple days, or the first few times you use your amp.

I mean the slow solvent/turpentine based varnish, not car paint type thinner based which is very aggressive and eats insulation out (don't ask how I found that :( ) nor a water based type which will rust and short everything.
 

Clyde

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #6 on: June 18, 2015, 11:26:10 AM »
Thank you, Mr. Fahey.  I'll give that a try.  Hopefully the environmental regulations in my part of the world still allow for such a product to be sold & used. :duh 

I've worked on a number of these amps over the years & own this 3005 & one of it's combo cousins, a 5005.  I love these both for sounds produced & simplicity of design (sort of).  Each one a bit unique in some quirky way and all sound wonderful to my ear.  The only things I ever seem to mess with are trying different op amps & changing the input resistor to 1M.  Everything else just seems to work as designed.  This one in the only unit that I've come across that had a trans 'issue'. 

I'll give this trans an oil varnish dip & post back with results.  Thanks again for the guidance. :dbtu: 

Clyde

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #7 on: August 12, 2015, 11:36:31 AM »
OK...late response on the outcome here.  I picked up a can of oil based marine spar varnish, removed & dipped the power trans.  Did the trick as far as 'noise'.  Plus, I get that new-boat-smell for a bit.  Makes me feel like I really got something new too.  The down side was that the varnish cost almost as much as one of the Hammond trannys.

And just to satisfy my own curiosity, I am going to order one of the Hammond 166L28 transformers & install it just to see how it works.  I'm not looking for any magic as far as tone or anything...just testing out a replacement for the stock unit to see how it works as far as functionality & maintaining what tone is already there.  The higher VA rated unit was my choice based solely on the 40VA rating of the original circuit.  Just gotta know.

Thanks again, JMF.

J M Fahey

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #8 on: August 13, 2015, 11:06:53 PM »
You're welcome  :cheesy:

As of the varnish, see that you actually used but a couple spoonfuls, only what's absorbed in or coating the outside layer, everything else goes back in the can, undamaged.

Not wasted, you can use it on whatever needs it at home, or even in the yacht you keep anchored at the Yacht Club:


Clyde

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #9 on: August 14, 2015, 12:42:53 AM »
Yup.  Why'd you buy a boat?  Well, I had this can of varnish...

DrGonz78

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #10 on: August 14, 2015, 02:19:36 AM »
I got a couple of amps laying around in the shop that could serve as excellent boat anchors!!  :lmao:
“A person who never made a mistake never tried anything new.” -Albert Einstein

Enzo

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #11 on: August 14, 2015, 02:45:03 AM »
Hell, I have a wife that keeps my couch from blowing away.


Of course, I guess I am holding down this stool her at work.

phatt

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #12 on: August 14, 2015, 05:12:55 AM »
Hell, I have a wife that keeps my couch from blowing away.


Of course, I guess I am holding down this stool here at work.
:lmao: :lmao: but  a bit :loco


Hum, some time later,,,,,,,,,,,So what led to the demise of that clever chap Enzo?,,,


His wife cut the safety to his workshop and picked up the insurance and now she lives the high life on a shinny yacht in the Caribbean. 8)
Phil.

phatt

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #13 on: August 14, 2015, 08:11:25 AM »
OK...late response on the outcome here.  I picked up a can of oil based marine spar varnish, removed & dipped the power trans.  Did the trick as far as 'noise'.  Plus, I get that new-boat-smell for a bit.  Makes me feel like I really got something new too.  The down side was that the varnish cost almost as much as one of the Hammond trannys.

And just to satisfy my own curiosity, I am going to order one of the Hammond 166L28 transformers & install it just to see how it works.  I'm not looking for any magic as far as tone or anything...just testing out a replacement for the stock unit to see how it works as far as functionality & maintaining what tone is already there.  The higher VA rated unit was my choice based solely on the 40VA rating of the original circuit.  Just gotta know.

Thanks again, JMF.

Hey Clyde,
              Just spent the last few weeks testing out many amp designs and also different size and voltage power transformers.

I'd say the difference from 40VA to 50VA is minuscule.
You would only be able to perceive this difference in an A/B test which is a lot of trouble to setup anyway.
A tiny bit more clean headroom is all that would happen.
just quietly,,,, your money might be better spent on a higher SPL speaker. :-X 8)

my 2 cents worth,,

Phil.

Clyde

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Re: Marshall 3005/Lead 12 Power Trans Question
« Reply #14 on: August 14, 2015, 11:29:17 AM »

Hey Clyde,
              Just spent the last few weeks testing out many amp designs and also different size and voltage power transformers.

I'd say the difference from 40VA to 50VA is minuscule.
You would only be able to perceive this difference in an A/B test which is a lot of trouble to setup anyway.
A tiny bit more clean headroom is all that would happen.
just quietly,,,, your money might be better spent on a higher SPL speaker. :-X 8)

my 2 cents worth,,

Phil.

Thanks Phil,

Here's the deal on these PT's for these amps.  The 3005/5005 Lead 12's are a few years old now & I'm seeing more & more posts in various forums about owners in search of replacements for whatever reason.  So, using one of mine as a test bed, I wanted to see what would be a reasonable replacement that fit specs & retained tone.  That lead me to the Hammond choices in my initial post.  Difference simply being the 1A/28VA unit vs the 2A/50VA.  Cost difference is fairly negligible.  I questioned the Marshall spec rating of 40VA but I figure that the designer had to have a reason. 

I understand the higher SPL speaker swap.  Micro-stack or combo version, these amps generally benefit from a speaker upgrade from the Celestion G10D-25's that came as issued.  My current experiment is based solely on a maintenance/longevity quest for a substitute part that I can honestly say: "Yes, I tried it & it works".  I don't have $$ to burn but this isn't much more of a cash outlay than auditioning a set of bass strings or tubes.  Still cheaper than a boat.  So far.