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

[J M Fahey]

I struggle with "blanket effect" since I've converted my amp.

Mmmmmmmmhhhhhhhhhhh !!!!!!!!!!! *That's* interesting.
Can you please post some schematic, even if hand drawn?
An "original version" one, plus mods duly annotated would be most welcome.

[Setneck]

Mmmmmmmmhhhhhhhhhhh !!!!!!!!!!! *That's* interesting.
Can you please post some schematic, even if hand drawn?
An "original version" one, plus mods duly annotated would be most welcome.

As confirmed by the guy at Bogner, to convert XTC 101A (6L6) to 101B (EL34) You only need to unsolder piggybacked bias resistors and change screen resistor values, OT and tubes. No modes to preamp or poweramp needed.


Regards, Andy

[J M Fahey]

So all you did was what you state above?
Changing bias and screen resistors should have no or very little influence on sound, you are simply giving the tube what it needs.
Changing tubes yes, 6L6 "have more teeth/bite"; EL34s are "middier, warmer, creamier", you name it.
The sound will change for sure, but it should not turn into "blanket in front of the speakers".
That leaves the OT as a big suspect.
*Maybe* the original Bogner OT was very high quality; why don't you try it again, with the EL34's?
Really the same transformer *can* and usually *is* used with both.
Maybe Bogner tweaks them *a little* but nothing drastic ... or they want to sell you an "original" one, instead of you spending your money somewhere else ... nothing wrong with that.
Worst case, get it back to original; after all the results were not what you expected, and once you start modding the mods ... you may waste too much time (and money) .
Of course, it's your amp, time, money, etc.
Good luck.

[Setneck]

Yes, the only changes were made as stated above, after contacting amp producer. They even said: every OT for 100W Marshall will do. So, if they've said that changing OT is essential - as it isn't only cosmetically tweaked but wounded somehow different - don't You think that it would be quite strange if they would advise me to change the OT if it wouldn't be really necessary? .

BTW, if it wouldn't be neccessary they could add a bias switch like in Mesa amps to switch between 6L6 and EL34. And there is no such possibility in Bogner amps (same as in Marshall amps and many others).

As I've already written - I have played for some time with original OT and the sound was not good. Boomy (tons of unneeded reverbish headroom), muddy (the distortion was unclear, the notes were hardly articulated) and completely crunchless. I have also a/b'd my amp with regular 101B (2 yrs older than mine so practically made from the similar components) with same speakers, same setting and same tubes: the sound was different, and the difference wasn't only in my ears. Regular 101B was crunchy, sweet sounding with notes jumping out of the speakers and chords like played by piano.

So, I bought used Dagnall D2668 and put it in the amp. After a change the sound came closer to regular 101B, especially crunch finally came there and boominess has gone. That convinced me that changing OT was however important. But after a few months of gigging I noticed that my tone is quite backed-off in band mix a bit more than it would result of low-mid-voicing of Bogner amps. Which is the thing I love in it and that is why I bought XTC. I only made a mistake buying 101A, but it occured that the mistake is to be fixed quite easily.

As I've said: the sound is very nice while playing all by myself. So, the OT is good but the amp sounds too "vintage" to me, and I want to make it more "modern". After conversion I've sold original OT, which was very high quality indeeed, but useless for me. The buyer have put it in his SLO copy and is very happy with it. It is another tiny piece of evidence for me that it was wounded rather for 6L6's.

And because of the facts that: there were rumours that MM is producing trannies for Bogner and MM OT's are being known as making the amps more open and more modern sounding, I am about to make a decision to buy MMO-PX-100 .

Believe me Mate, I am not a prince of persia having tons of $$ and don't like to waste my money at all . Simply I want to make my amp playing the way it can play. I have started with cheaper solutions and they didn't work in 100%, so, I'm afraid that the last thing to do is changing OT .


Regards and thank You very much for professional and competent input.

Andy

[dchang0]

If your amp tech can get his hands on a hi-fi-grade Edcor output transformer, you could try it on a test run. Oddwatt uses them for their KT88 monobloc tube amp kit--you could search for their schematic and lift the model number from there.

Overkill for what you want, but the frequency response is super linear from 8Hz to 20KHz. It'll actually probably make your amp too bright and transparent for actual use, but it's a way to prove that it's your OT and not the other components.

You'll get more bang-for-the-buck by swapping speakers, though. Even though speakers cost more than OTs, the change in tonal character is many times greater than with an OT swap.

[Gregg]

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 was also wondering how a T75 can "open" the sound...

[Steve Conner]

I think this guy needs to sell his Bogner and get one of these.
http://technabob.com/blog/wp-content...h-tube-amp.jpg

Except lose the iPod, you need a turntable to open the sound.

[Alex R]

"How Alice Undid the Blanket Effect"



You can't see it very well, but in her right hand is a 470pf bright cap she's about to solder across the volume control. Silver mica acourse.

[Setneck]

Alex R -> Thanks for the suggestion, I will consider doing that with my tech. As Bogner is low-mid-voiced amp that might help, and hopefully that would not change its tone character.

Gregg -> 75's opened my sound making it more crunchy and fuzzy (in positive way). V30's were brighter but less distorted to my ears, too clear, even a bit ice-picky. 75's have maybe less definition but made my sound more marshally-overdriven. I know that these are love-or-hate speakers - and there are more people that hate them than those who like them - but in my bandmix 75's sit better than V30's (great speakers anyway, which is pretty obvious)

dchang0 -> unfortunately no chance for me to get these trannies. But thanks for the tip anyway.

Steve -> that would be solution, but sometimes I play in places that have not enough space on stage for that sort of equipment. So, I'll however stay with my Bogner


Regards, Andy