marshall 2204 el34 to 6550

[blackie13]

Mary christmas to everyone!!

here's the deal...

I have a moded 2204 with some vintage glass (tungsram 12AX7 and RFT EL34's) and it has that vintage feel and compression that you hear in the vintage marshalls.
A few days ago I tested a pair of JJ E34L's and I can say that I like them as much as my RFT's...
The sound is surely different like way more headroom, less mids, less compression, more treble...

So I was wondering, since I enjoyed the change in the Power tubes, will the 6550 will be a nice choice for me...?
I know that I have to change some parts...I know an experienced tech who can do the job for me...

Has anyone of you went from el34's to 6550...??

Thanks in advance

 

[GCKelloch]

Maybe first have your tech bias the EL34L's to 70~80% dissipation to get more even harmonic warmth if that's what you find lacking. Those tubes can take a beating. You can also just run one pair to cut the power in half and plug the cab into (or set the switch) to half the cab impedance value to correct the tube load.

Not sure what you want from 6550's, but I'd probably try a pair of JJ KT77 biased to at least 70% if you want bigger bass like 6550. They should have sweeter highs than 6550, and maybe smoother mids -- the ultimate "neutral" EL34 type that also breaks up smoothly, but may require a resistor change to bring up the bias to 70% or so. KT77 are beam tetrodes like 6550, so they generate lower level 3rd harmonics than EL34 pentodes, which technically makes the harmonic structure more balanced when biased warm in a class AB design. Again, just try a pair if you don't need the full 100W.

 

[Racerxrated]

Mary christmas to everyone!!

here's the deal...

I have a moded 2204 with some vintage glass (tungsram 12AX7 and RFT EL34's) and it has that vintage feel and compression that you hear in the vintage marshalls.
A few days ago I tested a pair of JJ E34L's and I can say that I like them as much as my RFT's...
The sound is surely different like way more headroom, less mids, less compression, more treble...

So I was wondering, since I enjoyed the change in the Power tubes, will the 6550 will be a nice choice for me...?
I know that I have to change some parts...I know an experienced tech who can do the job for me...

Has anyone of you went from el34's to 6550...??

Thanks in advance

So, one thing to consider is the Transformers are designed for 34s. When Marshall shipped the amps with 6550s it was only out of necessity since the 34s were not holding up during shipping, and 34s were becoming unreliable. When you bias 6550s in a Marshall you are supposed to bias them like an EL34, so the transformer isn't stressed. But, ideally 6550s should be biased much higher for optimum performance. So unless you want to stress the OT you won't be getting the most out of the 6550s anyway.
But, if you are looking for less mids and more treble I don't think 6550s are the answer...they are very mid focused in a Marshall. They are more similar to 34s than they are different IMO. KT88s might be what you really want. Not sure what a tech would need to run them, they usually are pop in replacements in a 6550 amp.

 

[JMP2203]

you can try 6l6 too, i remember a Suhr modded 2203 with 6l6, i recomend sovtek 6l6wxt+

 

[psychodave]

I love 6550’s in 2203/2204 Marshall’s. More than EL34’s.

May have heard it, but here is my bone stock 2203 JMP with a Klon clone out front. Just guitar, pedal and cabinet. Amp has an Ei in V1 and Chinese 8th generation in V2 and V3. GE 6550 power tubes.

https://youtu.be/e6Uj_DBTe58

 

[blackie13]

I love 6550’s in 2203/2204 Marshall’s. More than EL34’s.

May have heard it, but here is my bone stock 2203 JMP with a Klon clone out front. Just guitar, pedal and cabinet. Amp has an Ei in V1 and Chinese 8th generation in V2 and V3. GE 6550 power tubes.

https://youtu.be/e6Uj_DBTe58

I have seen it dave...
about 100 times...

I think that I'll give it a shot...
The amp is a handwired clone so the transformer can take all tubes as far as I remember...

 

[FourT6and2]

What kind of mod does it have?

Only way to know if you'll like it is to try it. Pretty easy to change a few resistors to run those tubes.

 

[harddriver]

RFT El34's don't compress as much as a Mullard. They tend to have more Headroom. 6550's are kind of like a high powered more Heavy duty 6L6 beam forming element tubes. THe EL34 is a power pentode.

Since the amp is already setup for EL34's I would say try a set of EH6ca7, they are beam forming element like the original Sylvania's. They aren't built as well but nothing new construction is but they are decent and sound pretty good these days. Buy a tube that has normal or late distortion so they have max headroom and this should give you similar tone characteristics to the 6550 without modding your amp.

Another one to try it the KT77 they were designed to be a heavy duty EL34, they don't compress like EL34's. They are a Kinkless Tetrode design.

It's just a couple of resistors in the bias supply circuit, The amp needs more negative bias to run 6550's if you really want to try a 6550. The regular SovtekWE or Svetlana's(which are pretty much Sovtek) are decent new production 6550's similar to the plate structure of GE and Sylvania 6550's. Another tip is don't bias the 6550 beyond 50-60% dissipation they don't like a hot bias.

 

[FourT6and2]

Another tip is don't bias the 6550 beyond 50-60% dissipation they don't like a hot bias.

50-60% of what? Do you bias them as though they are 25w?

 

[harddriver]

50-60% of what? Do you bias them as though they are 25w?

NOS 6550's like a GE spec out around 42 watt plate dissipation but 35 watts is more reasonable for new production. I usually don't bias them beyond 50-60% of either 35-42watts just to be easier on the tubes. I doubt newer production can handle 42 Watts just because they are not as robust,it also depends on how high your plate voltage is, 510 DCV is going to run a tube harder than 450DCV. If you bias a 6550 tube to 70% plate dissipation they tend to loose their low end definition and high end detail from my experience but you are welcome to experiment.

I also forgot to add in the previous post that you should change the bias grid leak resistors from 220K to at least 150K but 82-100K is technically recommended. The Marshall engineers were fearful of a runaway bias condition(ie redplate) of the 6550's due to the impedance mismatch of the EL34 spec'd Output transformers. Marshall's that came with 6550's had 150K resistors and they work fine and keep the R/C constant close to the original frequency range of the 220K/.022uf.

 

[FourT6and2]

No what I mean is... these amps are 50/100 watt amps with OT spec'd for EL34s @ 25 watts of dissipation. So if you run 6550s, shouldn't you treat them as 25w tubes and not 35+? i.e. when you calculate your bias, you need to use 25w as the dissipation figure.

25w tubes
Vp = 500
65% = 32.5

35w tubes
Vp = 500
65% = 45.5

If you bias 6550s in a Marshall to 65% as though they were 35w, you'd actually be at 91% for the OT spec and 25w tubes. So while the 6550s can handle it just fine, you are stressing the OT. I've always been told regardless of the tubes you sub in, you need to bias them according to what the amp was designed for, and not for the tubes themselves. Because if you use 35w tubes, your amp isn't suddenly putting out 70 watts. It's still a 50-watt amp unless you change the transformer.

 

[GCKelloch]

AFAIK, Marshall 2204 run at ~400V. 6550 or KT88 are likely to sound more mushy than KT77 or 6CA7 at that voltage, since they were designed to run at higher voltage. The JJ KT77 and 6CA7 are direct EL34 replacements that won't risk overheating the OT. In fact, they should both put out only ~20W at 400V -- same as EL34. Hard to tell from the specs, but the JJ KT77 might be closer to 17~18W at 400V. Not a big difference.

Seems like the point of the 2203/4 sound is a clear bass punch and detailed high end that doesn't mush out the lead channel. I'd think the JJ KT77 would do that best, while offering more flexibility for 70%+ biasing to minimize the crossover distortion that grunges up clean tones regardless of how hard the tubes are pushed. The KT77 clean sound is also to die for -- big/tight/clear and less stiff than the EL34L.

The JJ 6CA7 are a bit darker -- like the standard JJ EL34 with more headroom and less compression that "tilts" the balance more toward the lows. One reviewer said he didn't like them in his JCM800 for that reason. Great in the HiWatt I had back in the early 80's, but those run at higher voltage, have an extra preamp tube and a more "HiFi" OT. The EHx 6CA7 are comparatively more-mushy/less-glassy. The GE 6CA7 beam tetrodes were actually designed as scaled down 6550. The KT77 is ultimately more versatile, and shouldn't be too bright at all at ~400V. Use a Sovtek 12ax7 LPS for the PI tube if you want more compression.

Jimi Hendrix actually used Tung Sol 6550's in his JTM100's near the end biased to 33% to minimize burn outs. You might notice the more grungy & midrangy sound in the Hendrix In the West and Rainbow Bridge performances.

 

[paulyc]

I love 6550’s in 2203/2204 Marshall’s. More than EL34’s.

May have heard it, but here is my bone stock 2203 JMP with a Klon clone out front. Just guitar, pedal and cabinet. Amp has an Ei in V1 and Chinese 8th generation in V2 and V3. GE 6550 power tubes.

https://youtu.be/e6Uj_DBTe58

I’m with you Dave, I prefer 6550s by a wide margin.

 

[JMP2203]

6CA7GE are incredible in marshall poweramps

 

[GCKelloch]

6CA7GE are incredible in marshall poweramps

Expensive though. There's also some confusion about branding. GE labeled the imported Mullard EL34 XF2 pentodes as 6CA7 -- considered the best EL34's by those who have tried them. Sellers may not know the difference off hand, but either are worth a try if you want to pay for a good pair.

 

[JMP2203]

yeah but i was talking about the fat bottle 6CA7GE - those are also great in class A sockets in mark amps

 

[cardinal]

All I know is that my stock 2204 has 6550 and sounds like what I’d expect a Marshall to sound. Works for me.

 

[GCKelloch]

Right. You can tell the GE 6CA7 beam tetrode by the how the glass sticks out over the base. I think I might have had those in my HiWatt. The Sylvania weren't as well made as time went on. The GE are very expensive and increasingly rare. A big gamble if you don't know you will like the sweet meaty sound. The JJ are so much cheaper. from what I've heard, I'd say the JJ 6CA7 are "harder" sounding, but some have reported they sound more open after warming up for a while. Eurotubes claims the JJ KT77 were actually reverse-engineered from a set of GEC KT77 they gave the JJ company.

 

[Loudness250]

My 84 4104 I bought used. It had a Tungsram and an RFT in it too! crazy. It also had 6l6's, but they were not original. I replaced with RFT el34's and biased. I like RFT power tubes but mine are new and biased.

 

[psychodave]

Right. You can tell the GE 6CA7 beam tetrode by the how the glass sticks out over the base. I think I might have had those in my HiWatt. The Sylvania weren't as well made as time went on. The GE are very expensive and increasingly rare. A big gamble if you don't know you will like the sweet meaty sound. The JJ are so much cheaper. from what I've heard, I'd say the JJ 6CA7 are "harder" sounding, but some have reported they sound more open after warming up for a while. Eurotubes claims the JJ KT77 were actually reverse-engineered from a set of GEC KT77 they gave the JJ company.

I have quads of the GE 6CA7 and Sylvania 6CA7, they both sound good. I think I like the Sylvania more though.

The JJ KT77 is okay, but I really like the new production Genelex KT77.