BAD SLO: Innards, Plate Voltage n Such

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LPMojoGL

LPMojoGL

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Had a tube intermittently going wonky on me, so got inside the SLO.
I've read the old SLOs had a plate voltage of 505v. Mine is 480v, measured from pin 3 to ground, power and standby on, with an 8 ohm load, all knobs at zero.
Pin 1 is grounded and tied to pin 8 with a 1 ohm resistor. Measuring across pins 1 and 8, I found one 5881 had a voltage reading of zero. Culprit!
After cycling thru my stash, I found I have 3 5881s that read 37mv, and 3 that read 27mv. I popped in a new set of matched 6L6s that read 37-40mv. Better.
Hooked it up and it sounds fantastic. Buttoned her back up and called it a night.
Thought I'd share in case anyone was curious, or wanted a reference on how to bias the SLO.

Edited to say, using an RFT in V1 and old Tungsram in V2, if anyone is curious. The clarity and character of gain is much improved over the stock JJs. Not night n day, or something you'd notice in a band setting, but much better when rolling tubes in an isolated setting.
 
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Great sounding amps. They lowered the plate voltage on the power tubes in the new version because there were issues finding consistent new production tubes at the old plate voltage IIRC. As in what is available new in quantity had too many failures.
 
The cheaper Sovtek wafer bottom 5881s always sounded best in the older SLOs I had. Even compared to the Mesa 415/Sylvania 6L6 GC.
I liked Chinese Bs in the pre.
 
Racerxrated said:
The cheaper Sovtek wafer bottom 5881s always sounded best in the older SLOs I had. Even compared to the Mesa 415/Sylvania 6L6 GC.
I liked Chinese Bs in the pre.
Click to expand...
I tried the Chinese tubes, and they sounded really good. Was my 2nd choice. I like the character of the Tungsram just a bit more. Total cork sniffing stuff. Lol
Need to get more 5881. So dang expensive now.
technomancer said:
Great sounding amps. They lowered the plate voltage on the power tubes in the new version because there were issues finding consistent new production tubes at the old plate voltage IIRC. As in what is available new in quantity had too many failures.
Click to expand...

Wondered why, and if it makes any difference in sound. My SLO has the now defunct Classic Tone transformers. I wonder if the newer Heyboer(?) are the same.
 
I also liked RFT’s best in the pre of my ‘89 SLO followed by ‘50’s Bugle Boy’s. The amp is surprisingly receptive to tube swaps vs other amps

For powertubes I liked most my various vintage US 5881’s (GE, Tung-Sol, JAN Philips, RCA, Sylvania), but I bet my west German and pre-Winged 6L6GC’s would also be great in it
 
On a sort of related, sort of not related note. I came into a couple of the Jet City 100 models for very cheap recently. I specifically remember Dave Friedman saying that the transformers in the amps are decent. But would it be worth my time to upgrade the output transformers on either of these if I'm going to mod it anyways?
 
Bad.Seed said:
On a sort of related, sort of not related note. I came into a couple of the Jet City 100 models for very cheap recently. I specifically remember Dave Friedman saying that the transformers in the amps are decent. But would it be worth my time to upgrade the output transformers on either of these if I'm going to mod it anyways?
Click to expand...
I think it depends on what you’re going for with the mods? I haven’t heard of any going bad…so they’re probably just fine.
If you just want to try for a different sound then sure you can experiment with OT changes but that can get spendy. Not sure it’s worth the expense to be honest
 
LPMojoGL said:
I tried the Chinese tubes, and they sounded really good. Was my 2nd choice. I like the character of the Tungsram just a bit more. Total cork sniffing stuff. Lol
Need to get more 5881. So dang expensive now.


Wondered why, and if it makes any difference in sound. My SLO has the now defunct Classic Tone transformers. I wonder if the newer Heyboer(?) are the same.
Click to expand...

I would guess the transformers are wound to the same spec so again if there is a difference it's probably not a huge one. I should actually look and see which transformers are in mine...
 
Racerxrated said:
I think it depends on what you’re going for with the mods? I haven’t heard of any going bad…so they’re probably just fine.
If you just want to try for a different sound then sure you can experiment with OT changes but that can get spendy. Not sure it’s worth the expense to be honest
Click to expand...
For sure, this would be more of a "for science" mod then trying to make it cost effective. Haha. I guess I'd be looking for a transformer that's as true to the SLO tranny as possible. I know a lot of guys used the Onetics transformers in the SLO-Clones. I wasn't sure how much difference that would make compared to the stock Jet City.
 
Bad.Seed said:
For sure, this would be more of a "for science" mod then trying to make it cost effective. Haha. I guess I'd be looking for a transformer that's as true to the SLO tranny as possible. I know a lot of guys used the Onetics transformers in the SLO-Clones. I wasn't sure how much difference that would make compared to the stock Jet City.
Click to expand...
Don’t quote me, but I’ve heard that if you want a Hi Fi type of OT like the original DeYoungs, Mercury might be the place to go. But they are expensive. I’d reach out and ask them. Onetics, I’ve played a Sloclone with them and it sounded like the HR100 I had, which is great but not the same as the SLO
 
Racerxrated said:
The cheaper Sovtek wafer bottom 5881s always sounded best in the older SLOs I had. Even compared to the Mesa 415/Sylvania 6L6 GC.
I liked Chinese Bs in the pre.
Click to expand...
It's funny how those old Sovteks sounded great in amps that were designed around them but like total ass in ones that weren't. A lot of Wizards came with 5881s in the mid 90's.
 
braintheory said:
I also liked RFT’s best in the pre of my ‘89 SLO followed by ‘50’s Bugle Boy’s. The amp is surprisingly receptive to tube swaps vs other amps

For powertubes I liked most my various vintage US 5881’s (GE, Tung-Sol, JAN Philips, RCA, Sylvania), but I bet my west German and pre-Winged 6L6GC’s would also be great in it
Click to expand...
Send em to me and I'll let you know!
 
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