KT66 in a Super Reverb?

[guitarcapo]

I have a matched pair of Shuguang KT66 tubes that I bought for another amp project. They ended up not working easily with that. (not enough negative bias possible without major work on the rectifier circuit.)

Anyway I was going to try them in my Super Reverb. I dropped them in and biased to around 35 mA. Sounded pretty good. A little more mid hump to the overdrive. A little more shimmer on the cleans. But when I cranked the amp it sort of sputtered and the rectifier tube made some flickering like it wasn't happy so I powered it down. It's a JJ GZ34S/5AR4.

I might give up on this ideaand just put the 6L6GC back in there and rebias....But can anyone comment? Solid state rectifier? Different rectifier tube?

I think the power transformer can handle the extra current draw of the KT66 tubes o.k.....I'm more interested in the rectifier issues.

[Rod]

Hummmm...We need an amp tech here to answer this question...There may be voltage issues with the power transformer

[guitarcapo]

Another odd thing was that they seemed to take about 10 minutes before I could get a stable bias reading. They kept creeping up. It might be something about the tubes because other tubes seem to take a lot shorter time.
I ended up going back to the 6L6GC because they seemed to have too much of that shimmer playing clean. The overdrive sounds were nice and with a throaty snarl but nothing I couldn't achieve with a pedal easier. I don't think they are as well matched for the output transformer either. A little lost headroom. I'll probably just keep them for a future tube project.

[Rod]

Wow...The tubes should of come up to bias within 5 seconds after turning the amp off of standby....I would not use those tubes in your amp....The JJ 5AR4 is the correct tube rectifier for the amp...If you use a 5U4 the current draw is different..A solid state rectifier will stiffin the amps feel and tone and make it harder sounding...One tube I do like for a few of my amps is the Tung Sol 5881...It's a real sweet sounding 6L6, and it won't give you any trouble...The Sovtek 5881 is a good cheaper alternative as well...The highs of these tubes is smoother than your average 6L6

[guitarcapo]

It's really weird...the bias current readings just slowly creep up and up and then get stable. I was assuming that it's just how they are made because they both do it and they are balanced in doing it. They sound good but because they are a 25 watt tube instead of 30 watt, I'm getting a little less headroom. I've used one of these in my tweed Champ copy and they sound really bright (probably because of an impedance mismatch with the OT) there.

Is the Tung Sol 5881 a 6L6GC or 6L6GB?

Right now it has some "Fender" labeled made in USA 6L6GCs and I think I'm going with those.

[Timbre Wolf]

Originally Posted by Rod

the 5881 is a 6L6 type...GC GB...doesn't matter

Of course it matters: the 6L6GB is only rated to dissipate 19W, whereas the 6L6GC is rated to dissipate 30W. Check out this recent thread.

The current-production New Sensor "Tung-Sol" 5881 seems to be produced as a direct sub for 6L6GC.

- Thom

[sunbrst62]

The current-production New Sensor "Tung-Sol" 5881 seems to be produced as a direct sub for 6L6GC.

the info in this link would indicate a direct subbing for 6L6GC may not be advised in certain cases
http://thetubestore.com/tungsol5881.html

[Timbre Wolf]

Originally Posted by sunbrst62

the info in this link would indicate a direct subbing for 6L6GC may not be advised in certain cases
http://thetubestore.com/tungsol5881.html

Yes - that is the TubeStore's CYA statement, in case New Sensor suddenly decides to conform to the original 5881 spec. (23W plate dissipation, rather than 30W).

- T

[sunbrst62]

Originally Posted by Timbre Wolf

Yes - that is the TubeStore's CYA statement, in case New Sensor suddenly decides to conform to the original 5881 spec. (23W plate dissipation, rather than 30W).

- T

Thanks, just so I understand, you're saying this copy referring to the reissue 5881 as 23 watts max plate dissipation is in error, and to be correct, should state 30 watts for the currently produced tubes carrying this name?

[lupa]

for the record I own a Holland amp that came stock with two 5881/6L6WGC(30 watt plate dissipation) wafer base tube, i had my teck put in tung-sol5881 re-issues; and they were all done with in one week. From my experience these tubes cannot handle 30 watts plate dissipation.
And all my research since has provided me with this information
take it for what it's worth:
6L6GC=30 watt plate dissipation
Sovtek 5881/6L6WGC=30 wpd
tung-sol 5881 re-issue=23 wpd
6L6(all other codes)=19 to 23 wpd

25 Watt tubes such as 6L6, 6L6GB, and 5881 are rated for plate voltage up to 400 volts.
30 Watt tubes such as 6L6GC, 6L6WXT+, and 6L6WGC are rated for plate voltage up to 500 volts.
The KT66 tube type is a 25 Watt tube rated for plate voltage up to 500 volts.

[1guitarslinger]

A quick note. Same way that NOS western manufactured 6V6s can handle plate voltages above their ratings, NOS TS 5881s can handle plate voltages higher than their rating if biased properly.

[Timbre Wolf]

Originally Posted by sunbrst62

Thanks, just so I understand, you're saying this copy referring to the reissue 5881 as 23 watts max plate dissipation is in error, and to be correct, should state 30 watts for the currently produced tubes carrying this name?

The 23 W rating is from the original Tung-Sol 5881. The Tube Store published that rating based upon the US-made original Tung-Sol specs. New Sensor does not publish ratings for their tubes, so I recommend you speak with an established tube vendor (Doug's Tubes is a TGP member who sells these New Sensor 5881), and find out what the current batch's ratings are. When I did so, I was told they are the same as their 6L6GC (30W, though that is also not published by New Sensor).

- Thom

[sunbrst62]

Originally Posted by Timbre Wolf

...and find out what the current batch's ratings are. When I did so, I was told they are the same as their 6L6GC (30W, though that is also not published by New Sensor).

Thanks, I don't know a thing about the Tube Store, have never done business there. I have seen this particular page from their site linked here, and could not remember what was discussed about their stated specs.

[guitarcapo]

Back to the OP....any ideas if KT66 tubes can be made to work in a Super Reverb?

[Analog Assassin]

I've run Chinese Kt66s in my Super reverb with no problem. I have heard of bias drift with them, though.