6550 in marshall...what to get?

[joolzriff]

i need to buy a quad for a marshall jmp and these 6550's are ''Pricy''!!....
could anyone reccomend me a good quad for a good price...
i couldnt believe the prices of 6550 compare to 6L6'S and EL34's that i have bought in the past in other amps.
is a 6L6 in the same family as 6550?? if it is maybe that would be a cheaper route in the future..
cheers
j

[Steve Snider]

I just put a quad in my Herbert of the imposter Tung Sol 6550s being offered by new sensor . They sound great to me. Not too expensive.

[StonerTone]

Originally posted by Steve Snider
I just put a quad in my Herbert of the imposter Tung Sol 6550s being offered by new sensor . They sound great to me. Not too expensive.

Where did you get them ? I want to try these and compare to my real Tung-Sols.

[Roccaforte Amps]

Originally posted by joolzriff
i need to buy a quad for a marshall jmp and these 6550's are ''Pricy''!!....
could anyone reccomend me a good quad for a good price...
i couldnt believe the prices of 6550 compare to 6L6'S and EL34's that i have bought in the past in other amps.
is a 6L6 in the same family as 6550?? if it is maybe that would be a cheaper route in the future..
cheers
j






For NOS, GE 6550's always sounded best in Marshalls.
However, I've used Sovteck (Reflector) made 6550's
in many different amplifiers with great results,
same goes for the EH KT88, great tube too.
The new TungSol 6550 sounds real good,
I can't comment on reliability yet, but
its built well.
All of these tubes are very reasonable,
you just have to try them.

[Steve Snider]

Originally posted by StonerTone
Where did you get them ? I want to try these and compare to my real Tung-Sols.


I got them from New Sensor. They should be available soon if not already.

[John Phillips]

I'd convert the amp to run EL34s like it was designed to :).

Standard 50 and 100W Marshalls were never originally intended to run on 6550s - there's no need at all for a tube of that power capability. They were only fitted for the US market at the request of the US distributor at the time, because of some 'reliability' problems with EL34s. This was most likely unneccessary, since those same Marshalls in most other parts of the world have always used EL34s.

6550s change the sound a lot - much harder, with more clean headroom and a sharper transition to distortion when it does eventually occur. You'll hear much more preamp distortion and less power amp distortion with them. Good if you want a really big metal tone (eg Zakk Wylde), but not if you want a more 'classic' Marshall rock tone.

Changing to EL34s will need a resistor in the bias supply circuit replacing (the rebias is outside the range of the trimmer), but that's all.


You could also convert to 6L6s/5881s. I'm not actually certain whether you'd need to change the resistor or not - I've never done this particular conversion (6550 Marshalls are virtually unknown over here), but the bias requirement is somewhere in between the EL34 and 6550. That will give a different tone again, but it's worth considering. Marshall did in fact use 5881s for a time in the mid-90s when good EL34s were not available in the sort of quantities they needed.

6CA7s are an option too - they're essentially a US equivalent to the EL34, and will need the same kind of rebias, but the tone is bigger and more 'American' - Van Halen used them in his Super Lead, FWIW ;) - and they have better life expectancy than EL34s if long-term cost is a consideration.

[Greazygeo]

Originally posted by John Phillips
I'd convert the amp to run EL34s like it was designed to :).

Standard 50 and 100W Marshalls were never originally intended to run on 6550s - there's no need at all for a tube of that power capability.

Not everyone prefers EL34's....I change all my marshall's over to 6550's right away and I don't play metal....the tone is much nicer IMO....

George

[Roccaforte Amps]

Originally posted by John Phillips
I'd convert the amp to run EL34s like it was designed to :).

Standard 50 and 100W Marshalls were never originally intended to run on 6550s - there's no need at all for a tube of that power capability. They were only fitted for the US market at the request of the US distributor at the time, because of some 'reliability' problems with EL34s. This was most likely unneccessary, since those same Marshalls in most other parts of the world have always used EL34s.

6550s change the sound a lot - much harder, with more clean headroom and a sharper transition to distortion when it does eventually occur. You'll hear much more preamp distortion and less power amp distortion with them. Good if you want a really big metal tone (eg Zakk Wylde), but not if you want a more 'classic' Marshall rock tone.

Changing to EL34s will need a resistor in the bias supply circuit replacing (the rebias is outside the range of the trimmer), but that's all.


You could also convert to 6L6s/5881s. I'm not actually certain whether you'd need to change the resistor or not - I've never done this particular conversion (6550 Marshalls are virtually unknown over here), but the bias requirement is somewhere in between the EL34 and 6550. That will give a different tone again, but it's worth considering. Marshall did in fact use 5881s for a time in the mid-90s when good EL34s were not available in the sort of quantities they needed.

6CA7s are an option too - they're essentially a US equivalent to the EL34, and will need the same kind of rebias, but the tone is bigger and more 'American' - Van Halen used them in his Super Lead, FWIW ;) - and they have better life expectancy than EL34s if long-term cost is a consideration.











You'll also want to change the feedback loop
over to 8 ohms.
Marshall used the 4 ohm tap with 6550's,
they have a higher drive requirement.

While you're in there, it wouldn't hurt
to also change the bias feed resistors
to 220K, EL34s don't sound good
with the 82K-150K bias feed resistors
used on 6550 equipped models.


6550's do sound good in Marshalls,
especially the 2 12" combos,
makes them fuller sounding.
Just FYI. Doug

[joolzriff]

ok....ive been doing some research and the EH 6550/KT88 is roughly $100 for a quartet thats in my price range...
they have a 6550 and a KT88....what is the difference in these 2 tubes?
ive never owned a 6550 pwrd amp b4 so i'm totaly dumb to this...
if u ask what tone i'm looking for its just a good rock tone not super heavy music....
and thanx to all who have reply'd to my thread
cheers
j

[85db]

You'll also want to change the feedback loop
over to 8 ohms.
Marshall used the 4 ohm tap with 6550's,
they have a higher drive requirement.

While you're in there, it wouldn't hurt
to also change the bias feed resistors
to 220K, EL34s don't sound good
with the 82K-150K bias feed resistors
used on 6550 equipped models.


6550's do sound good in Marshalls,
especially the 2 12" combos,
makes them fuller sounding.
Just FYI. Doug

I'm looking at the JCM800 schematics right now. Here are the resistor values:

For 6550: bias feed = 150k, bias supply in series with the pot = 47k
For EL34: bias feed = 220k, bias supply in series with the pot = 56k

Now, the conversion instructions I found on voodooamps.com say:

"1.) Locate the 47K resistor above the bias pot and solder another 47K in parallel."

Two 47k in parallel is 23.5k... Does this shortcut create an equivalent bias voltage? Are there any cons to doing it this way vs implementing exactly per Marshall schematics?

[QRSS]

great question! maybe get better results as a seperate thread in the "amp technical info" section?

i'm very interested as i need to convert one of mine for this very pricey reason(el34s~half price of 6550/kt88).

[drbob1]

Has anyone used the new KT77s in a 6550 Marshall? From the sound of things they should give a more EL34 tone without the hassles of rebuilding the bias?

[QRSS]

it's my understanding kt77s are a drop-in replacement for el34s. kt88s for 6550s. i'm runnin' 2 kt88s in my '80 2203 with no bias section mods. will kt77s bias in the stock range?

[stump]

I put KT 77s in my friend's 1983 50 watter and they sound great. They biased up about 35mv and sound fine... better than the 6550s.

[Lou Brush]

The new Tung-Sol 6550s are a good choice, and not too pricey. If you want to spend a little more, get the NOS GE 6550's as previously suggested.

I prefer 6550s over EL34s in Marshall amps. To my ear, they sound "bigger". The 6550s also perform better than EL34s if you use the Marshall low input jack, imho.

[kurtsstuff]

I'm currently using JJ 6L6's in one of my 1980 JMP 2203's with great success!

[908SSP]

To my ears EL34s are the sound of Marshalls. But my ears are tuned to the late 60s early 70s and to English rather then American bands.

[85db]

bump on the resistor values.

[Denyle_Guitars]

My 2203 has SED 6550's per Pete Cage's recommendation. The amp sounds great once the master volume is opened up but it's not what you'd call a bedroom amp.:)

[keano]

What does it mean to bias the amp hotter? I have heard this but don't understand it?

Also I heard from Myles rose at Groove Tube he prefers KT88 to 6550 as they are simialr but distortion ins't as harsh as 6550s?

and who is Pete Cage?

[Roccaforte Amps]

I'm looking at the JCM800 schematics right now. Here are the resistor values:

For 6550: bias feed = 150k, bias supply in series with the pot = 47k
For EL34: bias feed = 220k, bias supply in series with the pot = 56k

Now, the conversion instructions I found on voodooamps.com say:

"1.) Locate the 47K resistor above the bias pot and solder another 47K in parallel."

Two 47k in parallel is 23.5k... Does this shortcut create an equivalent bias voltage? Are there any cons to doing it this way vs implementing exactly per Marshall schematics?





Is it a 50watt or 100watt?

If its a 100watt, locate the white wire coming out of the power transformer. Where it connects to the board, there should be a 27K
resistor in series with this wire. If its not 27k, make it 27K.
Next, you should have a 47K resistor in series with the bias pot.
If its not 47K, make it 47K.
Change the bias feed resistors to 220K, and switch the feedback loop over to 8 ohms. (this is the purple wire mounted on the speaker selector, you'll move this so its connected with the yellow wire).
Bias the 34's and you.re ready.

If its a 50watt, locate the bias tap, this connection comes off the rectifier, and is on the PC board. The resisotor should be 220K for a 50watt (this is the same resistor you would change to 27K on the 100watt).
If its not 220K, make it 220K. Change the bias feed resistors to 220K,
and the resistor in series with the bias pot should be 47K.
Same thing on the feedback loop, should be 8 ohms for EL34's (this is the green wire on the selector, connect the purple wire to it).

PS, with modern tubes you might still have too many bias volts,
if it does, try putting a 100K across the 47K.
You can add another if you need to.

[jda]

If you can find and afford them, GE 6550s last a really long time.

[Mr. SD-1]

+1 the SED 6550s are great

[keano]

So on the SED aren't all power tube amps marked for breaking up sooner or later? Like Groove tubes are marked 1-3 or 4-7. If playing low volumes which is still loud MV3 and trying to get the Zakk tone would I want 6550 to break up sooner or later?

[Giga]

Another vote for the KT77's. I haven't tried it in a Marshall but I did put them in my VHT 2502 poweramp instead of the EL34's that are stock.

I liked the KT's much better, in fact with those in the sound and feel reminded me a lot of the 6550 equipped UL I had before

I think the KT's are quite a bit cheaper then the 6550's if cost is a concern.

Giga.

[85db]

If its a 50watt, locate the bias tap, this connection comes off the rectifier, and is on the PC board. The resisotor should be 220K for a 50watt (this is the same resistor you would change to 27K on the 100watt).
If its not 220K, make it 220K. Change the bias feed resistors to 220K,
and the resistor in series with the bias pot should be 47K.
Same thing on the feedback loop, should be 8 ohms for EL34's (this is the green wire on the selector, connect the purple wire to it).


Doug, did you mean 56k instead of the 47k for the one in series with the bias pot? The schematic I'm looking at (http://www.drtube.com/schematics/marshall/jcm800pw.gif) indicates the 47k is for USA (meaning 6550) and 56k is for UK (meannng EL34).

[yZe]

Tung Sol RI 6550

get them from SRS webstore at ebay

that @$$ brain won't leave you feedback, but he does have some good deals

[bonchie123]

If you like Groove Tubes I got one 6550-C performance rated for 6 that I have no use for. You can buy another 6 rated match pretty easily from any dealer. The other of the pair was broken when it was dropped so I have this 6550 thats brand new and no use for it.