Quicksilver 6550A's?

[lpd]

Ok I purchased a quad of NOS GE 6550A's for a very decent price and am wondering if these tubes will function in my Quicksilver KT88 monoblocks ok?

I have 2 Genelex KT88's and am searching for another pair at a decent price and until I find them at a decent price.....(hell still isn't cold enough), I thought I'd try the GE 6550A's.

My amps currently have stock Quicksilver KT88's (Chinese) which are ok, but nothing to brag about.

Any thoughts/opinions?

Thanks,

Peter

p.s. why are most NOS 6DJ8's noisy as hell??!!!!!!

 

[Burnedfingers]

Peter

All that is needed is to adjust your bias. The 6550's will work very well and you just might be surprised with the difference between the 6550's and the KT88's. Another good tube would be the Sovtek 6550 tube and there are naturally other brands that will work also.

J

 

[Burnedfingers]

p.s. why are most NOS 6DJ8's noisy as hell??!!!!!!

p.s. why are most NOS 6DJ8's noisy as hell??!!!!!!


I'm going to get into trouble on this one.


Because they are a junk tube!


Sorry Frank!

 

[Burnedfingers]

Peter

Do your Quicksilvers have 6DJ8's in the frontend? If so they are converted 8417 amps not the true KT88 version.

J

 

[lpd]

Burned,
My amps are KT88 monoblocks using a 12FQ7 in the front end. My pre-amp on the other hand (Counterpoint SA-1000 with a few mods) uses a 6DJ8 buffer, which depending on the tube can really change the tone of the pre-amp.

I have quite a few NOS 6DJ8's, Amperex (White label, Orange, Bugle Boy, and for good luck a Bugle Boy w/ a "D" style getter, Siemens, and a few other. Haven't tried new production tubes, but I'm about to as alot of the NOS tubes are noisy even though they test good. I currently am using a Philips 6DJ8 and am quite happy with its performance.

What do you recommend biasing the 6550As at? I biased my KT88's at 57.5ma/per tube, but thought I would run the 6550A's at 55ma? I have seperate bias pots for each tube (after the fact mod).

 

[Burnedfingers]

Peter

The separate bias is a nice touch especially if the tubes aren't matched perfectly. The difference sonically between 55mA and 57.5 mA will be zilch. The tubes will last longer at 110-115 per pair than at higher bias. With a distortion analyzer I was unable to see any difference between the 110 and the 125(per pair bias). Personally I believe the 6550's lose a little on the low end but more than make up for it the midrange detail.

J

 

[lpd]

The seperate bias taps are great as matched tubes (especially nos ones) are becoming harder to find.

I'll let you know how the GE's sound once I receive them.

 

[Burnedfingers]

Do you happen to have a hand drawn schematic for your KT88's? Mine used the 12BH7 for both tubes on the front end. I contacted Quicksilver only to be told that he didn't have a schematic for my version and it was special. I drew up a schematic for it and if I can dig it out will repost it otherwise I believe it is on a prior Quicksilver post.

j

 

[dshortt9]

I have a pair of 8417 monos that I have modified the bias to use anything but 8417's. Using KT90's with good results at present. I would appreciate it very much if you could mail or post the schematic so I can change my front end to use a 12BH7 or 6DJ8.

 

[richwalters]

yes J.....Interesting.....What B+ are you assuming at running 6550's at 55mA per tube in AB1 UL p-p ?????

rich

 

[lpd]

I'm not sure what the b+ in the KT88 monoblocks is, but I'm assuming its about 450-475 margin. I'll pull out the vm tonight and check the voltages.

 

[richwalters]

Okay at the bench- with my switchable B+ homemade amp. I'm running at 485V B+ using parallel P-P UL 2,25K A-A with 6550B's, just squeezing 135W per ch. Tubes reasonably well matched give excellent AB1 performance. I find 6550's give lowest THD at app 65mA/quies/ tube.
Another interesting situation occurs at reduced B+ of 250V using same circuit but 95mA quies /tube. At reduced Pout of 25W, Anode current =100mA per tube n'st damm it class A.
THD in both power cases well below 0.1% at 1dB below clip with 20dB fb..

enclosed excel graph..I hope this comes through.....my machine isn't the best to use..for attachments....


rich