B+ voltage

[billstets]

With all this talk in the thread about the Gitarre & Bass article, I was thinking that I should try a Marstran PT to get the voltage up to 450v. But before I do, can anyone chime in on what to expect? Tighter bass? Louder? Brighter? Thinner in the highs (don't want that!)? More headroom? If there's more headroom, does it still crunch nicely? I didn't want this to get lost in that thread, so I'm posting separately.

After my session last night, I'm questioning the new PT, because the 45 kicked butt! Although I wouldn't mind if it was louder!

Another question: just what was the standard B+ voltage in the JTM45? Someone posted on that other thread that the originals were 450v. Maybe it was a comment from the article, I forget. But if you look a the Germino site, he says that the volatges vary and he's offering a low voltage PT to delliver 410v. So were some 400 or so and otehrs 450+?

[arledgsc]

I think +450V is the historic JTM45 voltage but they varied down some over the years they were in production. I have read where lowering the B+ will give you a browner sound that can be very nice but if you run out of headroom sounds pretty bad. But I have no recent experience with vintage amps to compare. My B+ is 410V and sounds pretty good! Scott

[billstets]

I think +450V is the historic JTM45 voltage but they varied down some over the years they were in production. I have read where lowering the B+ will give you a browner sound that can be very nice but if you run out of headroom sounds pretty bad. But I have no recent experience with vintage amps to compare. My B+ is 410V and sounds pretty good! Scott

Is yours a Metro kit with the stock PT? I haven't checked mine since I built it. I can't recall what it was, but I suspect 390?

[Roe]

more generally, lower b+ will sound more compressed and middy. higher b+ will sound have more chime and punch. lows will be tighter

[robert]

Hi,

I've measured on some original, proper biased JTM 45 amps plate voltages around 480 Volt (heaters 6,4 Volt). And they did sound very good!

Regards

Robert

[Roe]

Hi,

I've measured on some original, proper biased JTM 45 amps plate voltages around 480 Volt (heaters 6,4 Volt). And they did sound very good!

Regards

Robert

that sounds rather high. what was the wall voltage? and which primary did you use?

[VelvetGeorge]

I settled on the lower B+ spec after listening to different voltages. At higher B+ the amp started sounding brighter and more modern to my ears. It lost some of the creamy, vintagey vibe IMO.
I felt the 8k primary OT and lower B+ combined for the best JTM 45 experience.

If you want more headroom and/or tighter tone I'd suggest using a 6.6k primary OT. That would keep the lower voltage feel and tone, while cleaning things up a bit.

That said, I'm sure Brian's PT are drop in replacements and will work perfectly.

george

[arledgsc]

Is yours a Metro kit with the stock PT? I haven't checked mine since I built it. I can't recall what it was, but I suspect 390?

No, I get 410V DC with the Mercury Magnetics -G2 and 323-0-323 volts AC output.

[billstets]

I think I'm going to pass on changing t he PT right now. It does sound really great the way it is, and I really only notice the flabby bottom if I dime it. But I don't play it dimed. I like the voumes at 6-7 and then I use boosts and OD pedals for more drive. At 6-7, it' easy to dial back to a nice clean sound too. When I dime it, it kind of melts down, and the bass get flatulent and whole thing is mushy, and a good clean sound is too far back on the guitar volumes for my tastes. I mean it's fun messing around with it dimed, but it's not usable for what I do.

[out of focus]

I did this swap.. Marstran 1202-55 for the stock Metroamp PT. I was getting 370DC before.. Now about 425DC.. The amp sounds a bit more Fenderish at lower volumes.. With the amp dimed I don't notice much of a difference ..I am keeping the Metro Transformer for my next build

[billstets]

I did this swap.. Marstran 1202-55 for the stock Metroamp PT. I was getting 370DC before.. Now about 425DC.. The amp sounds a bit more Fenderish at lower volumes.. With the amp dimed I don't notice much of a difference ..I am keeping the Metro Transformer for my next build

That's helpful. I'm keeping my Metro PT. One question: Is it any louder with the 1202-55? Or just more clean headroom?

[out of focus]

Not noticeably any louder to my ears..I do like that extra clean headroom though.

[neikeel]

I think I'm going to pass on changing t he PT right now. It does sound really great the way it is, and I really only notice the flabby bottom if I dime it. But I don't play it dimed. I like the voumes at 6-7 and then I use boosts and OD pedals for more drive. At 6-7, it' easy to dial back to a nice clean sound too. When I dime it, it kind of melts down, and the bass get flatulent and whole thing is mushy, and a good clean sound is too far back on the guitar volumes for my tastes. I mean it's fun messing around with it dimed, but it's not usable for what I do.

Suggest you swap out your PI output couplers for 0.047uF

If that is not enough change the normal channel small electrolytic for 1uF (if that is too extreme maybe 10uF )

[shakti]

I have been very happy with the Valve ARt/Shuguang KT66s that came with my kit back in early 2006 (probably the 11th gen that Tube Tramp swears by), they've been working flawlessly with hardly any bias drift, and I've been happy with the sound.

However, I've had a pair of smoked glass GECs laying around for a couple of years (they're going in my upcoming block logo build), and I tried those in my BB combo yesterday. It's a stock Metro kit except premium Sozos and Marstran PT, running 450V. WOW! I was knocked out. As I said, I've liked the Shuguangs, but the GECs are soooo much tighter in the bass, detailed and not boxy or cluttered in the mids, and treble is clear and sweet, not harsh at all. I was seriously blown away...Beano tone all the way. So some of that uncontrolled bass and mush at high volumes is the power tubes for sure.

Nonetheless, the higher B+ does really help controlling it a bit.

[Roe]

allegedly, the original pots have different taper so that it is easier to dial in low settings