NAD! '82 Marshall 4104 with EV's

  • Thread starter Thread starter 7704A
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7704A said:
Just checked, and it looks like 2/3, probably 3/3 of the preamp tubes are Winged C's. I've heard those are good? I don't take much sniff of cork so I'm not in the know.
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There's very little sound change with tubes of the same type. At least that can't be dialed around the tonestack.

Most of the appeal to vintage and NOS tubes is that they literally last forever.

There are certain types of tubes that are famous for imparting a specific sound, but it's relatively a small percentage of the whole
 
DanTravis62 said:
There's very little sound change with tubes of the same type. At least that can't be dialed around the tonestack.

Most of the appeal to vintage and NOS tubes is that they literally last forever.

There are certain types of tubes that are famous for imparting a specific sound, but it's relatively a small percentage of the whole
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With newer production/high gain amps I agree, tube rolling doesn't make much difference. But, in my exp with vintage Marshalls pre 1990 they are a noticeable change up when pre tube rolling.
And, in the OPs case, I'd HIGHLY recommend grabbing a pair of GE 6550s, bias them up and turn up...BIG difference IMO.
 
Also, when biasing 6550s in a Marshall you need to treat them like EL34s since the transformers are designed for them. So, between 30-40ma should be a sweet spot. That way the OT isn't stressed by 6550s biased up in the 50-60 range...not worth risking imo.
 
Racerxrated said:
And, in the OPs case, I'd HIGHLY recommend grabbing a pair of GE 6550s, bias them up and turn up...BIG difference IMO.
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Didn't expect to hear this from you. Are you a 6550 guy over EL34s? Or is it just a "GE" thang? lol
 
Racerxrated said:
Also, when biasing 6550s in a Marshall you need to treat them like EL34s since the transformers are designed for them. So, between 30-40ma should be a sweet spot. That way the OT isn't stressed by 6550s biased up in the 50-60 range...not worth risking imo.
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How would that stress the transformer?
 
7704A said:
How would that stress the transformer?
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The way I've read it, because the 6550 is a 40 watt tube, when it's in an El34 amp, that is designed for 25w per tube, when the 6550 is biased up to say 50-60ma it wants to pull that 40w from the OT but can't do that comfortably since the OT is designed around 34s that are 25w per tube. So the safe move is to bias the 6550 like an EL34, which would be around 30-40ma. That way the 6550 isn't trying to pull more watts from a transformer that isn't designed to run them.
Maybe someone else has a better way of explaining this, but it's basically 'better safe than sorry' with the Drake/Dagnall OTs that are EL34 based.
 
Racerxrated said:
The way I've read it, because the 6550 is a 40 watt tube, when it's in an El34 amp, that is designed for 25w per tube, when the 6550 is biased up to say 50-60ma it wants to pull that 40w from the OT but can't do that comfortably since the OT is designed around 34s that are 25w per tube. So the safe move is to bias the 6550 like an EL34, which would be around 30-40ma. That way the 6550 isn't trying to pull more watts from a transformer that isn't designed to run them.
Maybe someone else has a better way of explaining this, but it's basically 'better safe than sorry' with the Drake/Dagnall OTs that are EL34 based.
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Wouldn't that only become an issue if he was running it towards the upper volume range i.e damn loud? Forgive me, my electronics knowledge ends at 12v vintage chevy type wiring, lol

I had a 6550 loaded Plexi 100 watt but it's been too long to remember where it was biased. I wanna say 35ma but don't quote me. A TV-electronics guy I knew did the swap and he wasn't a player so everything was based around reliability rather than tone. It was definitely hammer-level reliable and still sounded good so I didn't have any complaints. I liked the 6550C's cause they broke up a little more smoothly and quickly than my Russian set, which still means a ton of headroom. I think I was paying $50 bucks a set for 6550C quartets on sale so I grabbed a couple sets and they lasted many years.

@7704A I could probably text my tech about that if you decided to go that route.

@glpg80 might have some insights. He seems pretty amp savvy.
 
The only difference between 6550s and EL34s in a push/pull class AB arrangement are a slightly higher plate impedance (4k vs 3.5k), slightly increased heater filament current demand (1.6A vs 1.5A), and the inability to run as high of a screen grid voltage with 6550s. Otherwise the tubes are close enough which is why Marshall substituted them for durability for as long as they did in the USA market.

IMHO the differences are a wash given how much variance tube to tube exists these days. Bias them however you please.
 
Racerxrated said:
The way I've read it, because the 6550 is a 40 watt tube, when it's in an El34 amp, that is designed for 25w per tube, when the 6550 is biased up to say 50-60ma it wants to pull that 40w from the OT but can't do that comfortably since the OT is designed around 34s that are 25w per tube. So the safe move is to bias the 6550 like an EL34, which would be around 30-40ma. That way the 6550 isn't trying to pull more watts from a transformer that isn't designed to run them.
Maybe someone else has a better way of explaining this, but it's basically 'better safe than sorry' with the Drake/Dagnall OTs that are EL34 based.
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Hmm, that doesn't quite match with my understanding of how tube power amps work, but I'm not an expert. It does give me some hints at what to look at in terms of theory and specs to figure out the reasoning behind the above though. Thanks!
 
7704A said:
Hmm, that doesn't quite match with my understanding of how tube power amps work, but I'm not an expert. It does give me some hints at what to look at in terms of theory and specs to figure out the reasoning behind the above though. Thanks!
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I'll find the thread/comments I've read about how to bias 6550s in Marshalls, and why. At the same time, I don't think I've read about OTs frying because of running 6550s at their normal bias points which are higher than 34s, so maybe it's not a big deal.
I guess I'm just a little on the cautious side after reading about this in other forums.
 
Racerxrated said:
I'll find the thread/comments I've read about how to bias 6550s in Marshalls, and why. […] I guess I'm just a little on the cautious side after reading about this in other forums.
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It’s on the internet so it must be true?

:D
 
DanTravis62 said:
There's very little sound change with tubes of the same type. At least that can't be dialed around the tonestack.

Most of the appeal to vintage and NOS tubes is that they literally last forever.

There are certain types of tubes that are famous for imparting a specific sound, but it's relatively a small percentage of the whole
Click to expand...
I agree with you, for the most part. At the volumes I play at 99% of the time, they don't make a huge difference. Certainly not as much as preamp tubes.

I have been surprised a few times by changing brands of power tubes, when cranking an amp.
The first time was when I replaced some el84s in a PV Classic 30. I was cranking the clean channel for plexi-like breakup. One set was more stout, with higher headroom and less breakup. Kinda meh. The other had way more saturation, less headroom and was more reactive to how hard I hit the strings. Very ACDC. Brand and build of tube? Or just where how they were biased in the circuit? Dunno.

I noticed the same thing with an Allen Classic 10, a 5F2-a, single-ended, Class A, 10 watt amp. It ran off one power tube. Swapping it had significant impact on the sound.

Based on @Racerxrated suggestion, I grabbed some GE6550s for my 4104. Unfortunately, they weren't matched, about 20ma apart. They ran ok, didn't have any hum or noise, but didn't sound as good as the Sovteks I replaced. I went to swap em out, and ended up using one of each, a Soviet and GE! lol. For some reason that combo sounds best.
 
LPMojoGL said:
I agree with you, for the most part. At the volumes I play at 99% of the time, they don't make a huge difference. Certainly not as much as preamp tubes.

I have been surprised a few times by changing brands of power tubes, when cranking an amp.
The first time was when I replaced some el84s in a PV Classic 30. I was cranking the clean channel for plexi-like breakup. One set was more stout, with higher headroom and less breakup. Kinda meh. The other had way more saturation, less headroom and was more reactive to how hard I hit the strings. Very ACDC. Brand and build of tube? Or just where how they were biased in the circuit? Dunno.

I noticed the same thing with an Allen Classic 10, a 5F2-a, single-ended, Class A, 10 watt amp. It ran off one power tube. Swapping it had significant impact on the sound.

Based on @Racerxrated suggestion, I grabbed some GE6550s for my 4104. Unfortunately, they weren't matched, about 20ma apart. They ran ok, didn't have any hum or noise, but didn't sound as good as the Sovteks I replaced. I went to swap em out, and ended up using one of each, a Soviet and GE! lol. For some reason that combo sounds best.
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Cranking the amp is when you'll hear the differences, if there are any. I was shocked at the differences between Siemens, Winged C and old Mullard 34s vs any JJ, EH, Sovtek etc. But at lower vol it's harder to tell. Modern amps don't seem to care much though.
 
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