Mercury Magnetics OT's - need to replace and need an advice

[Setneck]

Hi!

I think about replacing OT in my amp and think about two Mercury Magnetics output transformers: MMO-PX-100 and MMO-100C. Both are designed for hi-gain applications, but PX-100 is described as right for highest gain amps.

The goal is to remove the "blanket" effect (the amp sounds like the cabinet is covered with blanket). I want to improve my tone by removing it and open it up, I'm also looking for more "bite" and want it to sound sharper.

Does anybody dealt with one of those transformers and could tell me impressions?

Thanks in advance and best regards

Andy

[Chuck H]

Depending on the amp there may be a lot that can be done to the circuit before you shell out coin for transformers. Too often players think tone is ALL in the transformers. Tone is in every component. There's no more tone in the transformers than anything else. So while an improvement can be made by upgrading transformers, unless the ones you have are grossly bad the difference will be small. Snipping out or reducing the value of some treble bleed caps or a change of speakers is much more likely to do what you want IMHE.

Here's some reading material for you.

http://music-electronics-forum.com/t22606/

[Setneck]

Hi Chuck, thanks for Your reply. I know that changing OT won't make any miracles for my tone, and I actually don't need them. I only want to open the amp a bit and make it a bit sharper. I don't want to mess with the circuit (and I don't need that as the overall tone of the amp suits me very much), the thing is that original OT in my amp is the most probably faulty and for some reasons I have no chance for original replacement. There are the rumours that MM makes trannies for a company that produced my amp so MM seem to be a natural choice here IMO.

Regards, Andy

[ThermionicScott]

It might help if you shared what amp and speakers you've got! How in the world would we know if a particular "big high-gain amp" OT would be right for your application?

- Scott

[Pedro Vecino]

Which amp is?

[Setneck]

My tech just replied that OT installed in my amp is fully operational.

The amp is XTC converted from 6L6 to EL34 specs which basically needed changing changing OT and tubes . As it was impossible for me to get an EL34 replacement my tech have installed vintage Dagnall D2668 taken from old JCM800 2203 (not reissue). But after a year of using that combo it seems to me that this cool OT doesn't exactly match with hi-gain amp. The tone is very ok, don't get me wrong, but just too "vintage", quite backed-off. Very nice while playing myself, but in band mix (we play rock/metal tones, close to Dio/Sabbath Martin era) it's just too "old" .

Cutting long story short - it seems that Dagnall tames a bit modern character of my amp. What I don't like

I had the exactly the same thing while using all NOS tubes lineup (Tesla EL34's and Philips, Brimar & TFK ECC83's). The tone was perfect while I rehearsed only by myself - warm and round. But in a band mix I was hidden and dull. Changed power tubes to =C='s and preamp to russian Sovteks 12AX7WA & WB - the tone jumped out. But still it is not enough (even compared with regular 101B equipped with all Chinese preamps, which are very boomy sounding to me - but it is still more in-front than my amp). So, I just think that my OT - very nice to install in JMP or JCM800 - is not enough for my amp.


Regards, Andy

[Steve Conner]

I don't see why changing the tubes required a change of output transformer. EL34s and 6L6s are similar enough that the same OT should work well with either.

Maybe ask your tech to put the old one back in.

[Setneck]

I don't see why changing the tubes required a change of output transformer. EL34s and 6L6s are similar enough that the same OT should work well with either.

Maybe ask your tech to put the old one back in.

My tech was told by the guy from Bogner that changing OT is needed as they wound them a bit differently for 6L6. Funny, that they don't change anything in preamp or poweramp circuit. Only piggybacked bias resistor, OT and tubes. Even screen resistors in my amp were in EL34 values .

Besides I played for a while with original transformer and the sound was too boomy and muffled. So the OT for 6L6 is indeed wounded differently.

Regards, Andy

[Steve Conner]

OK, so you've already tried the original and didn't like it.

The PX-100 is supposedly "Great for JCM800s". To me that says it would sound similar to the Dagnall that you removed from an actual JCM800. Or maybe not.

Out of the two Mercury transformers, I'd pick whichever one is the biggest and heaviest. If it were me I'd go even further: Try a Hammond OT from their hi-fi range, not the new guitar range. You're making most of your tone in your preamp, and you want the power stage to deliver maximum bandwidth and as much clean power as possible.

Does the XTC have a presence control? Is it maxed? If there's no presence control, maybe you could have your tech modify it to add a fixed presence boost.

[Setneck]

Yes, the PX-100 is marked as great for JCM800's but also for "highest gain amps". And that is why I consider buying that one. Besides, generic JCM800 has less gain and B+ than my amp, and that can make specific difference as far as OT is concerned.

The XTC has Presence and I have set it at 2 o'clock. More gives a stiff and harsh sound.

Thanks for the input Mate

Regards, Andy

[J M Fahey]

The goal is to remove the "blanket" effect (the amp sounds like the cabinet is covered with blanket).

Switching speakers will have 10 times more effect than switching transformers.
You would only need to do that if your amp had been built with an OT wound as a power transformer: no interlacing at all, high parasite capacitance, high loss inductance, plus maybe tin roof grade iron, but if you already used a Dagnall, which *is* a guitar output transformer, and an old Marshall standby for that matter, with hundreds of thousands of happy users, I fail to imagine an*huge* difference in a Mercury Magnetics transformer.
Definitely not better than using a good, established Hammond transformer.
And one from their Audio/HiFi range, with lots of interlacing, best iron, high parallel inductance, low series inductance, low capacitance, will definitely go beyond any guitar transformer.

[Setneck]

Switching speakers will have 10 times more effect than switching transformers.

I've already done that - switched from V30's to G12T-75's what opened the sound, but still it's not enough.

You would only need to do that if your amp had been built with an OT wound as a power transformer: no interlacing at all, high parasite capacitance, high loss inductance, plus maybe tin roof grade iron, but if you already used a Dagnall, which *is* a guitar output transformer, and an old Marshall standby for that matter, with hundreds of thousands of happy users, I fail to imagine an*huge* difference in a Mercury Magnetics transformer.

As I've written above - I don't expect miracles by changing OT. I only suspect that my Dagnall - which is great OT indeed - simply doesn't handle hi-gain character of my amp. I struggle with "blanket effect" since I've converted my amp. Till now I've changed tubes, speakers, etc. The OT is the last point. And even if the change would be only slightly noticeable I still will have a good quality transformer in my amp. It won't be change for worse IMO so still it's worth to check if the change of OT will solve the problem.

Regards, Andy

[Pedro Vecino]

I would not worry about the OT using these preamp tubes (12Ax7WA/WB) in this amp. Sovtek WA, although are more lineal/open than the WB has too much compression. That kind of premature compression in overdrive crushes the pulsation response, reduces his speed and generates an scrambled texture. The WB is similar but his sound is under water. Itīs even more dangerous :-)
For me it's much better to use Chinese 12AX7 and after that you will refine the final response. You may use one (no more) WB to outline the rough/aggressive character, but you can use one or two ECC83JJ for this purpose at strategic locations.
This would not be my final choice but sometimes itīs necessary to have a good starting point (a reference). Using high-grade power tubes is also positive. Within the same model, lower grade tend to compress more.
Hope it helps

[Setneck]

Thanks Pedro for Your lines. I've gone thru' endless line of tubes, both NOS and current production. XTC is very sensitive to the tubes and it was first thing I messed up with.

As for the chinese - they are put stock into XTC but to me they sound boomy and muddy in that amp, making it very undefined. I much prefer WA's & WB's. WB indeed compress the tone quite much but I use it in V2 which is 2nd stage for 2nd and 3rd channel, 3rd stage for 3rd channel & in PI position, with great results. WA, as cleaner tube I use in loop driver and clean channel. In V3, which is 3rd stage for 2nd channel and 4th stage for 3rd channel I used to use chinese but I switched into Tung-sol RI. Both have similar gain amount, but Tung-Sol seem no to muddy the amp like chinese does. In V1 I use NOS Tesla E83CC, which gives the amp clean kick.

SED =C= in power amp.

Regards, Andy

[Steve Conner]

I've already done that - switched from V30's to G12T-75's what opened the sound, but still it's not enough.

Hmm.

V30s are famous for their piercing upper midrange and treble output. G12T75s have a darker sound with less high end, so they should have sounded more "blanketed". But you say the opposite, they sounded more "open". How do you explain this?

I think if you give this some thought, it'll help us (and you yourself) to understand what you really mean in objective terms when you say "open", "blanketed", "harsh", "stiff" and the like.