PT specs on Model T

[Ryanx]

my amp guy is helping me switch from 6550 to kt88 and is telling me to get some specs on the power transformer to make sure that this is going to be safe for my amp. 

can anyone (edbass, loudthud) give me specs on the PT and also anyone else's experiences good and bad with making the switch.

thanks!

[+Leo+]

I don't have specs for power transformer but I know that 6550 and KT88 are same tubes. 6550 is European name for KT88. Some people say that there is some difference in sound, nothing more. You don't need specs for that, just go for it, put the KT88.
I have also heard that KT88 sounds actually better then 6550 on Sunn amps, and I think that KT88 was originally in your amp.

Hm.. if your amp guy didn't know that, then you should think about changing your amp tech.

[Ryanx]

his concern came from the difference in i guess plate voltage and it's wear and tear from a hotter bias on my power transformer.  that being 30 some years old, he wanted to make absolutely positive that everything was in tip top shape, with running more power through an old transformer, he wanted to make sure it was with in the operable zone of the tranny.

[soberskipper]

his concern came from the difference in i guess plate voltage and it's wear and tear from a hotter bias on my power transformer.  that being 30 some years old, he wanted to make absolutely positive that everything was in tip top shape, with running more power through an old transformer, he wanted to make sure it was with in the operable zone of the tranny.

I would say that those old PT's are rock solid. If anything, the plate voltage issue would wear on the tube in which case you would just have to wait and see if one pops. The current draw of these tubes (6550/KT88) are so similar that the NEW issue makes probably draw a little less if anything. Bias adjustment necessary, but the only way to know if the tubes can handle it is to pop them in. Look at the tube spec sheets of the new makes you are thinking about.

Start the bias out pretty cold and move up slowly until your math says stop or you see redplate and come back down. Obviously if the PT is getting retardedly HOT, shut her down. You should be able to make a straight up swap with just a bias adjustment.

[Soundmasterg]

my amp guy is helping me switch from 6550 to kt88 and is telling me to get some specs on the power transformer to make sure that this is going to be safe for my amp. 

can anyone (edbass, loudthud) give me specs on the PT and also anyone else's experiences good and bad with making the switch.

thanks!

The KT88 historically is a higher rated tube than the 6550 and 6550A, and biases up very closely, though since the KT88 has a higher dissipation limit, it can take less negative bias voltage and still be in it's swwt spot. It also makes slightly more power. The new KT88's are not quite as good as the old ones, but they still usually have higher ratings than the 6550's, so I would say you should be able to put the tubes in, bias up the amp correctly for the new tubes, and be good to go.

Greg

[noel]

Sounds like this dude is trying to sell some iron and or more of his time.  KT88's and 6550 are equivalent.  Yes they might have minor differences based on brand, date of manufacturer etc. but they can be considered equivalent.  The other thing you gotta remember is most of the components in this amp have huge tolerances by today's standards.  The individuality if part of the charm of these amps.  You're smart to bounce this idea off the board though because unfortunately there's a bunch of techs who are either outright cheats or just don't know what they're talkinga bout.

[Ryanx]

i ended up bringing the 'T to a different tech who i will consider more credible on multiple levels, especially personally than my former.  He put the kt's in and was getting strange negative readings from the multimeter and it soon blew a fuse.  He pointed out that it looked as if one of my solder points was crazy but he wasn't sure.  I'm not positive on whatever really came of that, but i will find out with further testing i guess.  I feel glad retubing with the JJ's, finally replacing the junk Ruby tubes i had gotten originally with the amp 2 years ago.  Luckily i was in the position that i could drop a few extra bucks and picked up a set of ecc83s jj's and even a ecc81 for flavor.  I play guitar with the amp, but have always had an ecc81 in the phase inverter to clean up my sound with the hodgepodge i had going on tube wise in the amp.  He adjusted the hum balance, telling me that it's best described as a presence for the presence knob.  I've never heard that, any validity?  Replaced my fuse, tested it out, biased it somewhat cold i believe, but i'm not sure, my quad was rated to be biased at 34, though i'm not positive at what point it is at now. 

I will report back after testing today.

[Ryanx]

also, he was very happy to see the capacitors that i replaced from a list posted here for me.  he was impressed!