Tell me about KT88 tubes

[the guy who invented fire]

Re: Tell me about KT88 tubes

Well the problem is, There arent any good amp techs in my area that im aware of; thats why im not too sure I want to take it to just any music shop around where I live because I dont know what kind of rep the tech has

Where you are?

[Hellion]

Re: Tell me about KT88 tubes

KT-88s, from the limited experience that I've had with them, are an extremely powerful, dynamic tube. They sound clean with loads of headroom and it's difficult to overdrive them. A duet of 88s in A/B mode will push about 100 watts. If you're sold on EL-34s, my guess is that you're not going to really like the sound of 88s.

[Lake Placid Blues]

Re: Tell me about KT88 tubes

well my 800 is currently set up for 6550's and im not sure I want to mod any resistors so I can increase the bias range to accept EL34's. I might jus stick with 6550's

Have you tried some EL34s? Sometimes the bias pot has enough range to bias without the mod. As glassman said; KT66 is another option that may work. 6CA7s may work too.

[Luke Duke]

Re: Tell me about KT88 tubes

So, I sent an email to the people at "the tube store" and asked them if there was a 6550 tube that was closer to an EL34? and he said there wasnt any, but he said KT88 tubes are like an "EL34 on steroids." Im not big on the 6550's because of their harder attack and big, clean headroom. I like the 34's for their warm mids, early break up, and sweeter tone.

So, are KT88's anything like EL34's?


-Chris

\/\/\/

There is a lot to this question but in short, in a Marshall if you don't like 6550's you likely won't like KT88's...

Same big high headroom and same hard attack...

SOOOO true. I've got an 81 2204 and went from 6550s to KT88s. I preferred the 88s to the 6550s because they had a bit more of a bouncy sound.

NOS tube dealers but a set of NOS Tung Sol 6550's will run you $250 a pair ballpark...

If you want to use EL34's just have the mod done, it's a very common mod and many Marshalls have had it done.

Had Jeff Seal (a forum member here who owns an amp tech business speakersurgeon.com) mod mine. ....I also had him put in a souped up handwried turret board afterward. lol

If you like EL34's why not just stay with EL34's??

I'm with Christian, It's not a big deal to reverse.

[DonP]

Re: Tell me about KT88 tubes

You guys have your wires crossed.

6550's need MORE negative bias, so Marshall amps designed to use 6550's have the bias circuit designed to provide a more negative bias.

EL34's take less negative bias. You could slap the EL34's in there right now and the biggest issue would be if the EL34's ran too cold.

[Christopher Caruana]

Re: Tell me about KT88 tubes

You guys have your wires crossed.

6550's need MORE negative bias, so Marshall amps designed to use 6550's have the bias circuit designed to provide a more negative bias.

EL34's take less negative bias. You could slap the EL34's in there right now and the biggest issue would be if the EL34's ran too cold.

really??

[Lake Placid Blues]

Re: Tell me about KT88 tubes

The main difference between 6550 and EL34 set up Marshalls is the adjustmet range of the bias pot. Just take a volt meter and measure negative voltage at pin 5. Generally the range of the bias pot for 50 watt models is -38 volts to -48 volts set up for 6550's. Set up for EL34's the range usually runs from -34 volts to -40 volts. If the range is fairly close to that, you can probably run EL34s bias with a middle bias setting just fine without the mods.

On edit: another thing to do going from 6550 to EL34 is to change the NFB wire (purple wire to ohm switch) from the 4 ohm lug to the 8 ohm lug. This smooths up the amp highs and improves the clean tone too, BTW

[glassman]

Re: Tell me about KT88 tubes

Well the problem is, There arent any good amp techs in my area that im aware of; thats why im not too sure I want to take it to just any music shop around where I live because I dont know what kind of rep the tech has

Ask around. Talk to other that have had work done by your local tech to see if they felt they were served well. Ask the tech for references.

If that fails, find a tech elsewhere that you trust or has a good reputation and ship it there. This happens a lot. I got a 73 Super Lead in this afternoon from Florida for a full rebuild...that's 1000 miles away.

The key is to know exactly what you want...and having a tech that will walk you through the details.

[ginormous]

Re: Tell me about KT88 tubes

KT88's are a more-or-less straight swap for 7027A's. Those were used in Magnavox-era Ampeg amps in the early 70's, like the V4 head.

7027A's were very loud, lots of headroom, and rather hard to come by.

[Christopher Caruana]

Re: Tell me about KT88 tubes

Ask around. Talk to other that have had work done by your local tech to see if they felt they were served well. Ask the tech for references.

If that fails, find a tech elsewhere that you trust or has a good reputation and ship it there. This happens a lot. I got a 73 Super Lead in this afternoon from Florida for a full rebuild...that's 1000 miles away.

The key is to know exactly what you want...and having a tech that will walk you through the details.

well since mine is a VERY heavy combo, if I was going to ship it somewhere, I would probably have to end up unscrewing the chassis from the shell and just shipping that

[glassman]

Re: Tell me about KT88 tubes

KT88's are a more-or-less straight swap for 7027A's. Those were used in Magnavox-era Ampeg amps in the early 70's, like the V4 head.

7027A's were very loud, lots of headroom, and rather hard to come by.

I'd be really hesitant to recommend doing that without having a tech set it up. It's really easy to over-dissipate the screens in a V4, even using 7027As. JJ makes a really nice 7027A...in fact, I had a V4B leave the shop yesterday with a fresh set of them. The V4 is fixed bias that is non-adjustable so replacement tubes have to be properly selected.

well since mine is a VERY heavy combo, if I was going to ship it somewhere, I would probably have to end up unscrewing the chassis from the shell and just shipping that

That's the proper way of doing it. A tech doesn't need your speakers to repair/mod your amp though it is a good idea to let them know what your speaker combination is in case there are special considerations.