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Solid State Amplifiers => Amplifier Discussion => Topic started by: Clyde on June 16, 2015, 06:41:20 PM

Title: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde 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
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Loudthud 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: galaxiex 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?
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: phatt 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde 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
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: J M Fahey 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.
 
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde 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: 
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: J M Fahey 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:
(http://image.shutterstock.com/display_pic_with_logo/82831/82831,1165772180,1/stock-photo-expensive-wooden-yacht-in-the-harbor-of-geneva-switzerland-2302197.jpg)
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde on August 14, 2015, 12:42:53 AM
Yup.  Why'd you buy a boat?  Well, I had this can of varnish...
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: DrGonz78 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:
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Enzo 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: phatt 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: phatt 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde 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.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: J M Fahey on August 14, 2015, 04:05:41 PM
Quote
I'm seeing more & more posts in various forums about owners in search of replacements for whatever reason.
Not surprised at that.
People has itchy fingers and want to  "do something" , problem is the longest living part in those amps is the transformer (unless amp shorts and fuse is replaced by a nail ) , it's also properly rated so there's nothing to gain by going to a larger one.
Also does not wear, so maintenance is out of the question, longevity is granted unless grossly nuked the way I mention above.
Transformers are one of the very few examples of a perfect machine designed and built by Humans.

Spend that money in a 4 ohm Jensen MOD1050 speaker instead.
http://www.musiciansfriend.com/accessories/jensen-mod10-50-50w-10-replacement-speaker

Or similar 10 inch Eminence or Celestion if available in 4 ohms.

Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde on August 14, 2015, 06:59:02 PM
I have a 5005 combo that has a Celestion G10N-40 in it.  I wouldn't change a thing on that amp.  Love the sound. 

But now a question regarding speaker impedance.  The 5005 combo & the 3005 head/stack versions of these amps profess to have 8 ohm output load (the micro stack being 2 ea 16 ohm/parallel).  I was always of the understanding that in the world of solid state amps one never went below the 'rated' output impedance, lest the output transistors/power amp become toast.  These amps are ok at 4 ohms?
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: J M Fahey on August 14, 2015, 10:41:52 PM
Sorry, i should have been more detailed in my answer.

In 90% of SS amps, it's not safe to go below rated impedance (some have an extra power  and thermal reserve as in  Peavey) because it may put out some extra power if the supply allows so, but transistors can't handle it.
One big problem is that above rated current, transistor gain Hfe drops like a brick so asking double colector current may ask for 4 or 5 times more base current and you typically nuke the drivers ... milliseconds later the power transistors also die.

That said, in *this*  particular "12W" amp they used a 100W power stage  :duh

See for yourself:

Marshall 2200 a.k.a. Lead 100
100W RMS into 4 ohms, +/-40V rails, beefy enough to drive an output autotransformer , a single complementary pair TO3 metallic Motorola MJ2501/3001 (10 ampere, 150W 80V):
(http://www.drtube.com/schematics/marshall/2200-pwr.gif)

They used basically the same circuit , definitely same transistors in the 50W amp, then in the 30W into 4 ohms amp and this latest one was loaded with 8 or 16 ohms to tame it down to nominal 12W.
So one reason why this "little 12W amp sounds so BIG" is that it has a supercharged V8 engine under the hood ;)

30W @ 4 ohms:
(http://www.drtube.com/schematics/marshall/5203.gif)

so yes, the incredibly overbuilt "12W" amp , in this case, can easily drive 4 ohms loads and I always use them that way, sorry I forgot to explain why.
See that both use the exact same supply filters (2200X25) and roughly same voltage rails, the 12W uses +/-19V , the 30W unspecified but I guess 20/22V rails:
(http://www.drtube.com/schematics/marshall/3005.gif)

Also heatsinking is about the same:
(http://i681.photobucket.com/albums/vv176/GJonesy_2009/DSCN0643.jpg~original)
(http://i.imgur.com/rTE8bnv.jpg)

EDIT: in a nutshell:
a) they originally use 8 ohms speakers, (or 2 x 16 ohms)  so if you have original speakers or replaced them with other brand 8 ohms ones, fine, you have changed nothing except improve sound quality.
b) the amp design and parts used stands way more, I have personally loaded them with 4 ohms and got around 20V with no ill effects.
The transformers I tested were fine, warm but not *hot*  .
Same with heatsinks.
c) in theory you can turn that amp into a 50W or more one, *if* you provide better supply (beefier transformer and higher voltage electrolytics) and mount transistors in a "real" extruded finned heat sink, and adjust dropping resistors values to still feed +/- 15V to preamp.

I haven't modded original ones but straight built new ones, with the beefed up supply and heatsinking I mentioned, for killer 50/60W combos.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Clyde on August 15, 2015, 12:30:33 AM
And here I thought I knew something about these.  Many thanks for taking the time to post the details.  I never grasped the design relationship of these to their 50/100w cousins.  Supercharged indeed. 

Beautiful explanation.  I remain in awe...but learning.

Thank you sir.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: J M Fahey on August 15, 2015, 09:24:44 AM
You're welcome :)

I got *very*  intrigued when I found two TO3 metallic 150W transistors in a 12W rated amplifier, my only explanation is that they bought a Million for a very good price and then the 50/100W amps didn't sell, so they had to get rid of them one way or the other.

Or same happened to Motorola/ON and *they*  gave Marshall very good price and conditions.

The market for TO3 metallic Darlingtons dried up when excellent TIP142/147 became massively available .
Basically same specs, except somewhat less dissipation, they became the muscle in tons of Valvestate/Fender/Laney/H&k/Crate/Ampeg amplifiers.
I also use them ;)
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: just gear gas on October 19, 2017, 03:43:14 PM
Hi J M Fahey,
I came across this old thread and saw your knowledge about these amplifiers so maybe you can help me with one question:
I have a Marshall Reverb 12 that I want to modify to a head because mine comes withe  the 8" Marshall S300 Speaker wich sucks... The reverb 12 has you know shares the same basic circuit of the lead 12 with the addition of the reverb circuit but unlike the lead 12 is rated output is 12 watts into 16 ohm, I´ve  compared the schematics of the Lead 12 and the reverb 12 and, with the little knowledge that I have. the only difference I see is that r11 and r6 of the power amp section on the lead are ratted 1k and on the reverb (R35 and R36) are rated 220 on the Lead ther is also a condenser C6 ratted 22/25v that I cant find on the Reverb... Also the lead transformer voltage is 14,3 V AC  and the reverb is 21 V AC acording to both schematics.
 I would like to modify the Reverb circuit to 8 Ohm speaker output, since I only have 8 ohm cabs and I will be using the amp at full blast not bedroom level I want to make sure that I will not blow anything...
Can you help me on this?
Thank you
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: just gear gas on October 19, 2017, 03:46:33 PM
Hi J M Fahey,
I came across this old thread and saw your knowledge about these amplifiers so maybe you can help me with one question:
I have a Marshall Reverb 12 that I want to modify to a head because mine comes withe  the 8" Marshall S300 Speaker wich sucks... The reverb 12 has you know shares the same basic circuit of the lead 12 with the addition of the reverb circuit but unlike the lead 12 is rated output is 12 watts into 16 ohm, I´ve  compared the schematics of the Lead 12 and the reverb 12 and, with the little knowledge that I have. the only difference I see is that r11 and r6 of the power amp section on the lead are ratted 1k and on the reverb (R35 and R36) are rated 220 on the Lead ther is also a condenser C6 ratted 22/25v that I cant find on the Reverb... Also the lead transformer voltage is 14,3 V AC  and the reverb is 21 V AC acording to both schematics.
 I would like to modify the Reverb circuit to 8 Ohm speaker output, since I only have 8 ohm cabs and I will be using the amp at full blast not bedroom level I want to make sure that I will not blow anything...
Can you help me on this?
Thank you
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: J M Fahey on October 20, 2017, 03:21:23 AM
Just saw this when going to sleep (4:20 AM here) so too foggy to answer, but will do tomorrow.
Take care  :)
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: just gear gas on November 03, 2017, 10:33:14 AM
Hi J M,
If and when you have the time to address my question I would much appreciate it, you are the only Marshall lead 12 expert I came across that could really help me...
Thank you
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: orjfor on November 16, 2018, 04:41:35 AM
Hi I guess this thread is dead since no one has written in for at least a year but i give i a try.

I have a Marshall 12 Micro stack and I thinking about changing speakers in it and also add the capacitor mod in it. I also got an idea to put a clipping stage in it by adding two diodes and a switch to handle it with. Is it possible to add it after the R8 resistor? See attatched Pictures of the pre stage and a clipping stage. I know that it is clipping stages in other Marshall SS amps
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: phatt on November 17, 2018, 01:48:36 AM
I guess it's possible but you will likely effect the max volume available.
It would likely need a recovery stage. And still may not be what you want.
Frankly just get a dirt pedal in front would be a lot easier and there are many to choose from. 8)
Phil.
Title: Re: Marshall 3005/Lead 12 Power Trans Question
Post by: Synkopy on January 04, 2020, 10:10:36 PM
EDIT: in a nutshell:
a) they originally use 8 ohms speakers, (or 2 x 16 ohms)  so if you have original speakers or replaced them with other brand 8 ohms ones, fine, you have changed nothing except improve sound quality.
b) the amp design and parts used stands way more, I have personally loaded them with 4 ohms and got around 20V with no ill effects.
The transformers I tested were fine, warm but not *hot*  .
Same with heatsinks.
c) in theory you can turn that amp into a 50W or more one, *if* you provide better supply (beefier transformer and higher voltage electrolytics) and mount transistors in a "real" extruded finned heat sink, and adjust dropping resistors values to still feed +/- 15V to preamp.

I haven't modded original ones but straight built new ones, with the beefed up supply and heatsinking I mentioned, for killer 50/60W combos.

Sorry to revive an ancient thread. But I came into possession of one of these amp heads recently and wanted to thank you so much for this. As I’ve managed to do just what you’ve described. Upgraded electrolytics, bigger transformer, upgraded heat sinks, and rectifier, and adjusted drop resistors. Also made a small capacitor change to tame the fizzy top end and added an op amp socket for good measure. This little dude can easily keep up with my 60W blackstar now!