KT66 vs KT88

[SteveH]

Gents,
Opinions please ! I need to pick a quad to go with for my new ST70. I have heard very good things about the SED Winged -C- KT88's....But I recall reading somewhere that KT66's are the way to be.

Thanks !
Steve

[Bob01605]

If you have a stock ST-70 with a stock power transformer understand that KT88's or 6550 tubes will draw more current from your power transformer. The stock ST-70's power transformer was really marginal with that amp and many old ST-70 power transformers have hum, buzz and vibration issues. Personally I wouldn't use KT88's in an ST-70 with an original power transformer.

If your new ST-70 has an updated power transformer from Triode or Dynakitparts then KT88's are an option. Both of their power transformers are rated at 5 amps per channel instead of 3 amps like the original power transformers.

One of the nicest sounding tubes for the ST-70 are the JJ KT77's. Unfortunately, many are beset with manufacturing defects like undersized and poorly soldered pins. I was lucky and got a good quad from Jason Pang at Newquestsound. They are excellent sounding tubes. Another nice EL34 that some overlook are the EL34's from ElectroHarmonix. They are only about $40 - $45 a quad - one of the least expensive EL34's around but very good sounding with an especially nice, clear top end.

The SED winged =C= tubes are nice also - more expensive (maybe $70 a quad) than the ElectroHarmonix tubes but IMHO don't really sound any better for near double the price of the ElectroHarmonix EL34's.

I know others will have other opinions ..

Bob Latino

[SteveH]

Thanks Bob. My 'new' ST70 has the new triode PA060S, a 500mA choke, and dual 5AR4's....So hopefully I can suck down some current Yellow_Light_Colorz_PDT_02

[erichayes]

I talked with Bob Pletka of Eurotubes about a year and a half ago regarding the "skinny pin" issue with the KT77s, and he said that all those shipped after September, 2006 will have the proper (for the US) pin diameter. They are basically "drop-in" subs for the EL34 as far as bias and plate voltages are concerned, even though it's a beam power tube--as opposed to the EL34's being a power pentode.

The KT66, being basically a mutant 6L6GC, will have to be rebiased to prevent self-immolation. You'll want to see somewhere around 48~50 mA cathode current per tube, which should happen when you have around -40 volts on pin 5 of the tube(s).

[EWBrown]

The J/J KT66s (also available through Bob Pletka and Eurotubes), are supposed to be pretty good. I haven't tried these, so I can offer no relevant comments about their sound quality. They're definitely "mutant" 6L6GCs in every sense of the word :o

These J/J KT66s have a different shaped bottle than traditionsl KT66s, they look more like fat little KT88s. YMMV, etc.

/ed B in NH