Replacement tube options for JTM 45 RI..

[Melodyman]

Just picked up a JTM 45 RI and wanted to retube it with something better than the Sovtek 5881/6L6WGC it comes with. Trying to figure out which this is.. a 5881 or a 6L6? I would like to just replace them with a better quality tube for now without any mods needed and dont know which other brands offer a direct replacement.
The sticker on the inside of the amp says replace only with 5881 tubes.. but which ones? Can I plug in a set of 6L6GC's?
Thank for any help.

 

[Jonathan Wilder]

Just picked up a JTM 45 RI and wanted to retube it with something better than the Sovtek 5881/6L6WGC it comes with. Trying to figure out which this is.. a 5881 or a 6L6? I would like to just replace them with a better quality tube for now without any mods needed and dont know which other brands offer a direct replacement.
The sticker on the inside of the amp says replace only with 5881 tubes.. but which ones? Can I plug in a set of 6L6GC's?
Thank for any help.

5881/6L6/KT66 will all drop into the same amp. While the amp will have to be rebiased as it would whenever replacing power valves of any type, there will be no mods needed to bias any of these 3 valves in that amp.

KT66s, like all the other KT66 valves, are a bit pricey ($99.99 a pair) but to me they sound like a cross between an EL34 and a 6L6. More like a "6L6 that 'breathes'".

The Valve Art KT66s are a little cheaper at $79.99 a pair and sound awesome in a JTM45.

The JJ 6L6s are priced around $49.99 a pair and are your cheapest bet. I haven't heard them, but they probably sound better than the Sovteks.

The Winged =C= 6L6 is priced around $59.99 a pair. These are a really good sounding 6L6.

I can get the KT66 and the 6L6 in JJ, and in Winged =C= I can get the 6L6 at the above mentioned prices.

 

[MartyStrat54]

Adding a little to what Jon said. A 5881 is a 6L6. It's just an industrial number for a 6L6WGB. It is a short version of a regular 6L6. The KT66 is a British version of the American 6L6. Also, a 6L6GC is a more powerful tube. You can use it, but you won't be getting the full potential out of the tubes. If it was me, I would go with the KT66's.

What are your thoughts on the preamp tubes?

 

[guitarmartin416]

this seems to come up alot... I'm goin with the KT66's also!

 

[Hank Moody]

Just get the VA KT66's - I've been using a pair and they are still going strong after 2 years.

 

[jcmjmp]

If you go for KT66 tubes, the Gold Lions are the considered to be the best current production tube. Better bass and sweeter crunch.

You should also consider replacing the OT with a MM RS replacement.

 

[Birk]

I've put JJ KT-66 in my JTM45 RI, sounds good!
But I have to re-check/adjust bias again, due to the problems I've had explained in another topic.

 

[Melodyman]

Thanks for all the advice .. I guess what i'm trying to figure out is what the hell is a 5881/6L6WGC?
I ordered a set of Tungsol 5881's to pop in.. but the discalimer page on the tube site says its a 23 watt tube and may not work in my amp if the plate voltage is too high..
So I ordered a set of Winged C 6l6GC's to pop in but now I hear they might not work either.
I can only find one manufacturer of this mystic 5881/6L6WGC and that is the Sovtek thats in there. Isnt there another direct replacement tube that will replace the Sovteks with the same requirements? What did Marshall expect people to do if they cant find the sovteks? Where do they set the bias for this tube at the factory?
I am planning on getting the Metroamp conversion kit for this amp soon and I will swap out the board, OT and indeed will use the Gold Lions at that time. Until then, I just wanted a better set of tubes to play thru for now since these have been in the amp since 2006 when it was made. even tho its been in the box since then.
I have a 20 year old Blues breaker combo. It came with 6l6GC's and I had it converted to KT77 gold lions with JJ Ecc83's. Also put a pair of G-12 H 30's in it. It puts out 48 watts. it must have been an early one since the back panel says "Tremelo 50W" and has no writing for which jack is which (spkr/trem).. What did they do to reduce this amp now to only 30?

 

[Jonathan Wilder]

Thanks for all the advice .. I guess what i'm trying to figure out is what the hell is a 5881/6L6WGC?
I ordered a set of Tungsol 5881's to pop in.. but the discalimer page on the tube site says its a 23 watt tube and may not work in my amp if the plate voltage is too high..
So I ordered a set of Winged C 6l6GC's to pop in but now I hear they might not work either.
I can only find one manufacturer of this mystic 5881/6L6WGC and that is the Sovtek thats in there. Isnt there another direct replacement tube that will replace the Sovteks with the same requirements? What did Marshall expect people to do if they cant find the sovteks? Where do they set the bias for this tube at the factory?
I am planning on getting the Metroamp conversion kit for this amp soon and I will swap out the board, OT and indeed will use the Gold Lions at that time. Until then, I just wanted a better set of tubes to play thru for now since these have been in the amp since 2006 when it was made. even tho its been in the box since then.
I have a 20 year old Blues breaker combo. It came with 6l6GC's and I had it converted to KT77 gold lions with JJ Ecc83's. Also put a pair of G-12 H 30's in it. It puts out 48 watts. it must have been an early one since the back panel says "Tremelo 50W" and has no writing for which jack is which (spkr/trem).. What did they do to reduce this amp now to only 30?

You need not worry about the plate voltage. The BBRI only has a plate voltage of 420VDC...if their 6L6s can't handle that they shouldn't be on the market.

I think they're more worried about some of the amps that exhibit a B+ in excess of 500VDC.

And the 30 watts is more than likely due to the plate voltage along with probably a different OT plate load. However, volume-wise you're not gonna hear a difference between 18 watts of power. The amp just might break up a bit earlier. The BBRI that I overhauled with KT66s had MORE THAN enough volume at the supposed 30 watts.

 

[MartyStrat54]

Again, a 5881 is a 6L6. A 6L6 is a very old tube and there are different power ratings on different models. However, modern amps use either 5881's or 6L6GC's. The 6L6GC's will sub for a 5881, but it won't go into hard tube overdrive as it is a 30 watt tube and the 5881 is a 23 watt tube. Also, the 6L6GC is designed for high plate voltages. Let's just say it it the bad boy 6L6.

And you have plenty of choices for tubes in your amp as have already been pointed out. Any 6L6 tube will work as long as it is rated at or above a 5881. The KT66 will work and there are three brands to choose from.

So I wouldn't get into a panic. There are plenty of tubes that this amp will run. I will say that some people like a 6L6GC in place of a 5881, as it does provide a different sound due to the fact that the tube is not working hard. Some players prefer this sound. However, as I said, if it were me I would go with the GLKT66's.

 

[bencalhoun]

GUUUUYS!!!
Finally I think I may have found the thread!!!
I also have a bbri that says "50 watt tremolo" on the chassis.
I want to know is this amp really 30w, or 50w???
I dont have an o-scop, but if someone in this crazy world knows an actual answer, I may very well twirl like an obsessive compulsive psycotic ballarina....or not.
As far as I can tell, there is no difference, they only made 50w versions in the late 60's. The bbri only says it to be "historically accurate". (thats what Korg USA had to say about it, anyway). Is the thing 50 or 30 watts???? It makes a huuuuge difference as I want to put Celestion Blues in it! 600$ in speakers requires confidence in the fact. PLEASE HELP!!!!

 

[jcmjmp]

So which tubes did the OP go for?

 

[MartyStrat54]

I hope he went with your suggestion. GLKT66.

 

[cudamax2343]

Kool Thread. What kinda plate voltage will put the 6L6GC into overdrive?
Will 450dcv do it or does it need 500dcv and what about the KT-66?

 

[Jonathan Wilder]

Kool Thread. What kinda plate voltage will put the 6L6GC into overdrive?
Will 450dcv do it or does it need 500dcv and what about the KT-66?

With enough grid drive ( which most guitar amps have WAY MORE than needed) they'll overdrive at any plate voltage. However, the lower you go, the less headroom you have and as such an amp with lower plate voltage will clip more than an amp with higher plate voltage when played at full crank. But the difference between low and high would have to be at least 75 volts or more to really hear a night and day difference between the headroom of low vs high plate voltage.

Power supply sag comes into play here too. Plate voltage drops as plate current rises, and once the valves are drawing enough plate current to tax the supply, the total supply voltage will drop. A less efficient supply with lower filtering and a less efficient transformer will sag more than a supply with stiff/tight/lots of filtering and an efficient power transformer. The amp with the most sag will exhibit a compressed/squishy feel to it whereas the amp with the stiff supply will have a much tighter feel to it.

 

[cudamax2343]

What Marshalls have side by side spacing for the KT-66's besides the JTM-45 & the VM?

 

[Melodyman]

Hi All. 'I went with the Gold Lion KT66's and Tung Sol Ecc83/12AX7
along with a Metropolous PTP 66 era board with the MM 045RS-L coming soon.
So far its a big difference.. I have to do some more gigs with it to really dial it in, but so far its Big Tit Honey!

Bencalhoun: It appears that the earlier reissue BB amps were indeed 45-50 watts depending on which tubes it came with and some other changes... Mine came with 6l6GC's and put out 47 watts on the bench. I changed it to KT77's now.. super loud.. much louder than the JTM 45 RI.

 

[cudamax2343]

I hope he went with your suggestion. GLKT66.

So the almost double heater current draw on the KT-66's is not an Issue?
900ma to 1.5 amps per tube. Thats 1.2 amps more per pair.
The Tungsol KT-66's don't and pull only as much as a 6L6.

 

[Jonathan Wilder]

So the almost double heater current draw on the KT-66's is not an Issue?
900ma to 1.5 amps per tube. Thats 1.2 amps more per pair.
The Tungsol KT-66's don't and pull only as much as a 6L6.

Actually, check your data sheets again. KT66 heater current draw = 1.3 amps, so it would be 0.8 amps more per pair.

The JTM-45 and Bluesbreaker power tranny heater windings will handle it. This has been done on MANY of these models with stellar results. I just did one a few months ago, and the KT66s did not pull the heater voltage down at all.

Heater current only becomes an issue if the transformer cannot source the additional current. If it wasn't up to the task of sourcing additional current, the total heater voltage would drop as soon as you turned it on in standby. On these amps this is not the case.

Another thing interesting about the BBRI is that they actually used an output transformer with the proper plate-plate load for 6L6/KT66 valves (they've been known to use loads too low for the plate voltage used in their EL34 amps). Upon measuring the one I replaced with the Mercury Magnetics RS clone OT, the stock one measured out at 7.6K plate - plate load.

 

[cudamax2343]

Kool and I got that Info from this
John Templeton's KT66 Tube Reviews
A one John Templeton's. He did a review on KT-66's. Don't know if its true or not and was trying to find out if it is. Anyway's I did atleast find out that some of the KT-66's do draw alot more than other Kt-66