Hi,
I've been running an amp that was really designed for 6L6s on KT88s for awhile, with around 420V on the plates. I'm wondering what sonic/feel changes one should expect from raising the voltage? I've heard that those tubes "really feel more comfortable at around 500V," but I've yet to hear a single complaint from my tubes as they are.
Just curious...thanks!
What to expect from a B+ raise
Moderators: pompeiisneaks, Colossal
Re: What to expect from a B+ raise
That's such a vague statement about 88's, but I've heard it too. Most designs in the 500vdc+ range with KT88s run the screens lower, but not always.
In general any tube that can handle a higher voltage will give similar sonic results: more headroom (increased wattage), brighter tone, and more punch (i'm not sure if this is just a combination of the former two).
I've actually built the same amp with a B+ of 420vdc, and another with 500vdc. The latter was louder, brighter, and less smooth. I preferred the higher voltage, but only because I was looking for more headroom and dynamics. Depends on what you're after.
In your amp I'd be more concerned that the PT can handle the extra current draw from the KT88s, especially the heaters, if it really was 'designed for 6L6s'. But hey, sounds like it's been just fine.
In general any tube that can handle a higher voltage will give similar sonic results: more headroom (increased wattage), brighter tone, and more punch (i'm not sure if this is just a combination of the former two).
I've actually built the same amp with a B+ of 420vdc, and another with 500vdc. The latter was louder, brighter, and less smooth. I preferred the higher voltage, but only because I was looking for more headroom and dynamics. Depends on what you're after.
In your amp I'd be more concerned that the PT can handle the extra current draw from the KT88s, especially the heaters, if it really was 'designed for 6L6s'. But hey, sounds like it's been just fine.
Re: What to expect from a B+ raise
I've always seen the KT88 used as a way to maximize low end and wattage while safely running at higher voltages since they can handle it and not break a sweat. Where a similar tube (6550) would start to be pushing it's limitations, putting it's stable longevity into question.
The voltages given in recommendations outside of Data sheets is often like the 70% bias rule. It works safely for most things but it's not law. Use your ears, and monitor the tube if it's with in safe operating limits it's OK.
The voltages given in recommendations outside of Data sheets is often like the 70% bias rule. It works safely for most things but it's not law. Use your ears, and monitor the tube if it's with in safe operating limits it's OK.
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iknowjohnny
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Re: What to expect from a B+ raise
I went from a PT that got me 424 on the plates of a pair of EL34's to a PT that went 55 volts higher. I couldn't tell any difference to be honest.
Re: What to expect from a B+ raise
The 6 KT88's in my Weber AB200 bass amp runs stable with 650 V at the plates, 600 V at the screens and 40 mA idle cathode current. It can take it, and it sounds very clean with lots of bass available if needed..
Re: What to expect from a B+ raise
I've got an amp with a multi tap pt, switchable on the fly from 420 on the plates to 320 or so, running 6V6's. Even though the clean output level gets pretty much cut in half, if you didn't see that switch get thrown, you'd actually be pretty hard pressed to tell the difference. Once you start to listen ffor it, you can feel it, just a little punchier on high voltage and a little mushier on the lower voltage setting (this is with it cranked up). It makes a difference, but remember the old Fender schematics that come with the caveat that the voltages may vary by +/- 20%. Tubes are not picky eaters.
Life is a tale told by an idiot -- full of sound and fury, signifying nothing.
...in other words: rock and roll!
...in other words: rock and roll!
Re: What to expect from a B+ raise
For those of us who have experimented with power scaling / VVR will say that IF the pre amp voltages are kept nearly constant and the signal feeding the output tubes is adjusted (made smaller using a MV), and the bias is tracked, as the OP tubes voltages are dialed down the change in tone is minimal.
Change in pre amp voltages have a more significant change in tone IMHO.
Change in pre amp voltages have a more significant change in tone IMHO.