Old Marshall JCM900 found with 6L6 tubes

[Robert S.]

Re: Old Marshall JCM900 found with 6L6 tubes

I would have to hear the reason he gave for sticking with the 6L6s, especially since they are not the tubes the amp originally came with. I would think that a good amp tech would know the pin designations, heater and bias requirements for all the major tube types and putting that amp back to spec should be an easy task.

I'd get a second opinion. A Marshall with 6L6s? What does that sound like, a pissed off Deluxe Reverb?

j/k

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

although being an easy task, any local tech that would have help to do it, will at least charge me a vampire price because its considered "modding"

How nice .. I gotten a Marshall with 6L6s .. way to start a new year

 

[Robert S.]

Re: Old Marshall JCM900 found with 6L6 tubes

Thats not right. It shouldn't cost more than an hours labor. I mean come on, its a PCB amp so any additional components needed are most likely piggybacked on to the exsisting components. If there are any component changes made at all they should be very easy to see and to remove.

I'd keep asking around until you find someone honest to do the repair, if you can even call it that. Its really just a retube and rebias in my book.

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

yeah man. Thanks
I'm looking around for a tech to rebias the amp .. I tested the amp out for about an hour or so .. it sounds kindda good to me.
I hadn't have the chance to listen to a EL34 equipped Marshall yet, anyway I don't use their stock distortion. I use Xtreme Art effects, I wonder will EL34 make a drastic change in the tone .. hmm =)

 

[Lake Placid Blues]

Re: Old Marshall JCM900 found with 6L6 tubes

The original Marshall prototype and many real early production models used American spec 6L6/5881s. Most Marshalls prior to mid 67 used KT66 tubes, so I don't find a problem with a 6L6 Marshall. This is particularly true of master volume amps where most of the overdrive/distortion is generated in the pre-amp anyway. A slightly cleaner power tube per volume level, will improve the amps clean tone, and it will probably amplify the tones of effects devices better. This is particularly true of time delay effects. Moreover, the 6L6 has more low end punch. However, the EL34 will start giving some power tube overdrive a bit earlier and be precieved as louder.

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

The original Marshall prototype and many real early production models used American spec 6L6/5881s. Most Marshalls prior to mid 67 used KT66 tubes, so I don't find a problem with a 6L6 Marshall. This is particularly true of master volume amps where most of the overdrive/distortion is generated in the pre-amp anyway. A slightly cleaner power tube per volume level, will improve the amps clean tone, and it will probably amplify the tones of effects devices better. This is particularly true of time delay effects. Moreover, the 6L6 has more low end punch. However, the EL34 will start giving some power tube overdrive a bit earlier and be precieved as louder.

I think I would agree to your last statement.
For a 100watt amp, I believe that its going to be REAL LOUD at perhaps 2 or 3 but it isn't. My Fender Twin reverb is 150watts and at 2½ my room is about to shake, but hey .. the JCM900 even at 3 or 4 its still not as loud as I thought it would be.

Oh well, I ain't sure what to do now because I don't wanna be sliced by those techs when they rebias the amp to EL34s. But if its REALLY REALLY recommended that the amp should go back to what really belongs to it, then I will take it to the tech and make it an amp to be remembered.

 

[ErikH]

Re: Old Marshall JCM900 found with 6L6 tubes

That amp looks in good shape. Robert is right, those are not the tubes that amp came with. If you like the sound with 6L6's stick with them but leave open the idea of EL34's. It's not totally PCB. The tube sockets are hard wired. Everything else is PCB. After seeing the inside of mine and how neatly it was done, I can handle that. It's been very reliable anyway.

Funny that the tech you talked to considers putting the tube type it came with back in as "modding". It's more like "restoring" to me.

But again, if you like the tone of the 6L6, stick with 'em.

EDIT: Does it say "Hi Gain Dual Reverb" below JCM900 on the face plate? Its blurry but it looks like it to me. If that is the case, then check the year this amp was made. It may have come with 5881's stock. Those came with EL34's from 1990 through late 1993, early 1994.

As for the loudness, Twins have 2x12, this amps is 1x12. Give the 900 one more 12" speaker and it'll keep up better.

 

[Lake Placid Blues]

Re: Old Marshall JCM900 found with 6L6 tubes

It's too bad you live 1/2 way around the world away, because I'd bias your amp for free, if you supplied the EL34's. Biasing is not difficult really, and I think it's a bit unethical for some of these so called techs to slice people up so much. If the amp seems overly low on power now, then it may not be biased correctly for 6L6's even right now. I have found that Marshalls (and Fenders too) with some modern production 6L6's don't seem to be quite as loud as with EL34's or old stock 6L6 though.

It's hard to make judgments about power output from one amp to another, as so many varibles effect precieved loudness. One big factor is the number of speakers, and their effiency, and the physicality of the cab. Furthermore, master Volume amps with high gain pre-amps, pass a very compressed signal on to the power amp section, so what's 3 on one amp at a given settings is different from another. It's rarely linear. Compounding this, is the fact that the JCM900's padd the signal between the pre-amp and the power amp for the effects loop, and an op-amp brings the signal back up at the master control, just before the phase inverter stage.

If you use a lot of effects and don't usually use the amp cranked up really really loud as part of your overdrive tone, then I don't think you will notice a really big difference by going to EL34's as oppossed to staying with 6L6's.

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

EDIT: Does it say "Hi Gain Dual Reverb" below JCM900 on the face plate? Its blurry but it looks like it to me. If that is the case, then check the year this amp was made. It may have come with 5881's stock. Those came with EL34's from 1990 through late 1993, early 1994.

As for the loudness, Twins have 2x12, this amps is 1x12. Give the 900 one more 12" speaker and it'll keep up better.

There..
It indeed says "hi Gain dual reverb"
How do I go about requesting what year is it made in ?
And which year does the JCM900 comes with 5881s ?

arghhh
I wanna move to the US !!!

 

[Lake Placid Blues]

Re: Old Marshall JCM900 found with 6L6 tubes

Look on your serial number. After October 1992 the serial numbers changed to an all numerical nine digit code. The first two digits indicate the Year. The last two digits indicate the Month. So if it's like 95xxxxx03, it would be March of 95.

If it's prior to Oct 92 then it will have several capital letters at the beginning. The first letter after a space is the letter code for the year, the first two or three with a slash indicate the model number code. For example X/X Z xxxxx would be from 1992 and 1991. Y indicates 1990.

If its after mid 1994 it probably came with 5881s.

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

..... where on earth can I locate the serial number ..
I notice a white piece of bar code sticker behind the amp with this number written just bottom of the bar code:
972645527

Could this be the serial number ?
Thanks

 

[ErikH]

Re: Old Marshall JCM900 found with 6L6 tubes

What you have there is a 1997 Hi Gain Dual Reverb combo. It came stock with 5881's so having the 6L6's is not a problem, just a simple rebias.

I will tell you this, and several techs have told me this. Changing from 5881's or 6L6's to EL34's will require a resistor change (4 actually, 1 for each tube). Every tech I've talked to, even my own, has said the same thing.

LPB: I thought the swap to 5881's occured somewhere in late 1993 to early 1994. I could be wrong though.

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

gosh .. then I'm conned by the salesman.
See my topic is "OLD" JCM900 found ... blah blah

So i thought is was as "OLD" as the early 90s, Darn it , if i knew i won't even consider getting it. So just a resistor change for each tube will do ?? Nothing more than that

 

[ErikH]

Re: Old Marshall JCM900 found with 6L6 tubes

gosh .. then I'm conned by the salesman.
See my topic is "OLD" JCM900 found ... blah blah

So i thought is was as "OLD" as the early 90s, Darn it , if i knew i won't even consider getting it. So just a resistor change for each tube will do ?? Nothing more than that

It technically is old. Almost 9 years.

From what I've been told, yes, just a resistor change. If you like how it sounds now, keep it the way it is. Other than the 6L6's being in there it's essentially stock.

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

any diff between the 5881 and 6L6s ?

 

[ErikH]

Re: Old Marshall JCM900 found with 6L6 tubes

any diff between the 5881 and 6L6s ?

Dunno. I never played a 6L6 loaded Marshall. Only EL34, 5881 and 6550. I prefer the EL34's but everyone has different tastes.

Maybe Zerb will chime in when he wakes up. :laugh2:

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

I'll then experiment with the 5881s also,
i realize that the current vintage reissue Marshall uses 5881
Think the current ones ain't as good as the last time, but I guess since they use 5881 now I believe it isn't so bad

i'm just comforting myself . duh

 

[DesertRose]

Re: Old Marshall JCM900 found with 6L6 tubes

I managed to take the darn tube outta there amp.
I didn't know that it was that simple, i had the idea that I gotta unscrew the top and then do some stuff before I can pull the tube out

here's a pick of it .. I hope those Marshall users ain't pissed off when they see this