Fender Bassman 300 Watt Pro All Tube Bass Amp- KT 88's

Lonesomedave · #1 10-15-2011, 09:59 AM

well, here is today's stupid question.

anybody know or have thoughts about whether you can use KT 88's in this particular amp?

i posted another thread on the subject generally of KT 88's vs 6550's, and the consensus was generally, you can USUALLY substitute KT 88's for 6550's but better be very careful about the other way around... ie putting 6550's in an amp designed for KT 88's. this amp comes with six 6550's as it's power tubes.

but there was some comment about being careful, and matching plate voltages etc.

bottom line, does anybody have any experience actually doing it, or know how it would work out?

Mr. Foxen · #2 10-15-2011, 10:03 AM

Entirely depends on the amp.

someparts · #3 10-15-2011, 11:06 AM

Should be able to do it. You first, haha. As far as if the transformers and guts can handle it, etc. I don't see how the 300 wouldn't be a good candidate...that iron is HUGE.

I'm wondering if the amp would run cooler with the KT88s, or if the KT88s themselves are more tolerant of heat by design compared to 6550s? These amps are built like tanks but they build up a lot of heat without a fan.

BassmanPaul · #4 10-15-2011, 11:40 AM

you should be able to install KT88s but they won't be plug and play. You will have to set the bias appropriately.

Lonesomedave · #5 10-15-2011, 12:34 PM

Quote:

Originally Posted by BassmanPaul

you should be able to install KT88s but they won't be plug and play. You will have to set the bias appropriately.

gotcha... i wasn't going to try anyway. i'll have them installed and biased by a local amp shop that has many years of experience on tubes etc.

Mr. Foxen · #6 10-15-2011, 01:54 PM

Also, different KT88s have different specs, plenty are basically 6550s in different shaped bottles. The current draw is the bit where they can melt your amp.

BassmanPaul · #7 10-15-2011, 02:17 PM

Both tube types have 1.5 to 1.6 amp heaters so current draw should not be a problem.

bassboysam · #8 10-16-2011, 06:15 AM

I had EH KT88s in my 300PRO and there were no issues, granted I have no idea if the EH KT88 is a true KT88 or a 6550 in a KT88 bottle.

Mr. Foxen · #9 10-16-2011, 06:24 AM

Quote:

Originally Posted by BassmanPaul

Both tube types have 1.5 to 1.6 amp heaters so current draw should not be a problem.

The GEC is 1.8 amp. It is what other KT88s wish they were, so it is important to check the spec sheets: GEC KT88

the mojo hobo · #10 10-16-2011, 07:22 AM

I did have a problem with my Sunn 300t where the heater wiring became overheated and burned out at the connection to the power tubes circuit board. This was with Winged C 6550 tubes. I don't know if they inproved that in the Bassman or not.

Lonesomedave · #11 10-16-2011, 09:21 AM

Quote:

Originally Posted by bassboysam

I had EH KT88s in my 300PRO and there were no issues, granted I have no idea if the EH KT88 is a true KT88 or a 6550 in a KT88 bottle.

Quote:

Originally Posted by Mr. Foxen

Also, different KT88s have different specs, plenty are basically 6550s in different shaped bottles. The current draw is the bit where they can melt your amp.

ok, bearing what Foxen said in mind (that i have to watch out for excessive current draw)

who makes REAL KT-88's and not just 6550's in a KT-88 bottle?

does anyone know anything about Genalex? how about Tung-sol?

if I do it, obviously I want the real thing

bassboysam · #12 10-16-2011, 09:25 AM

the only one I am sure of is the JJ KT88

Mr. Foxen · #13 10-16-2011, 09:39 AM

Check the spec sheet, the GEC I link is the reference for the KT88, not sure what the top 6550 is. The Shuguang KT88 are pretty good, recommended by Chambonino. But,t he good ones might have the high current draw. There is a big extent to which they are functionally equivalent, but basically, its all in the spec sheet, and there are other factors affecting your tone, its an expensive way to o it.

Lonesomedave · #14 10-16-2011, 09:41 AM

thanks Bassboy;

there is a seller on ebay called AK6r, who sells a lot of tubes and who has helped me before. I have emailed him the qx about this very discussion we are having and if you like, i will post his answer when he gives it.

ps-edit- ok, thanks also Foxen; see post above; i will be real curious to see what ak6r says. he really seems to be knowledgeable about this sort of thing in the past.

bb5000 · #15 10-16-2011, 09:44 AM

I've tried Shuguang, Sovtek & GoldLion in my KT88 Weber amps. The Shuguang KT88-98 & Sovtek runs fine at 660 V plate and 600 V screen in the AB200... The Gold Lion (new production Russian tubes really) runs at 510 V plate and 505 V screen in the 6S100.

A 6550 has a screen voltage limit of 400 V and would probably not last too long in these amps...

Lonesomedave · #16 10-16-2011, 09:50 AM

bb5000;

yeah, but we are talking about going the other way; any thoughts about kt-88's in this amp, which has 6550's stock?

bb5000 · #17 10-16-2011, 10:01 AM

Quote:

Originally Posted by Lonesomedave

bb5000;

yeah, but we are talking about going the other way; any thoughts about kt-88's in this amp, which has 6550's stock?

Any amp designed for 6550's will not exceed KT88 specs regarding plate and screen voltage...most likely the Fender (Sunn) 300T has a screen voltage of ~350 V.... no problems for a KT88. Current draw is similar , tube primary impedance as well. My earlier comment was questioning the "6550 in a KT88 bottle" statement..I'd be reluctant to put 6550's in my amps.

CapnSev · #18 10-16-2011, 10:13 AM

What about the monster KT120s? Could they be substituted in a 6550 amp?

bb5000 · #19 10-16-2011, 10:27 AM

Quote:

Originally Posted by CapnSev

What about the monster KT120s? Could they be substituted in a 6550 amp?

If the power transformer can handle the extra heater current draw (100-300 mA / tube)...and if the bias voltage range suits the KT120....

Lonesomedave · #20 10-16-2011, 12:29 PM

ok, here is what Bob at AK6r had to say on the subject:

Dear straightflushwheel,

The real KT88's are the big bottle (not straight sided like 6550s) so they have bigger plate sections and are a stronger tube. The real KT88's are the JJ, Winged C, Valve Art, EHX, to name a few. The most popular one I sell for the best sound and price is the Genalex Gold Lion KT88 patterned after the legendary Genalex KT88's of the 1960's - it is ithe tube i use in all my high end audio tube sets. The JJ is also very good and a well built tube and would work well in the Bassman too and is slightly cheaper than the Genalexs. I have a few customers who have tried the KT88's and liked the sound and the bias setting is the same as for the 6550's so no changed needed there. The matched sextet of Genalex Gold Lion KT88's is in listing # 380222193207 for comparison. We also have the Bassman ULTRA tube set with the JJ KT88's and gold pin preamps in listing # 380377610816 in case you need a compete tube set rather than just the power amps.

Captain Bob