5U4G suitable for Dyanco ST-70?

Then again, one can also use 6L6 as a sub for the EL34 and four of those would cut the current draw enough to allow use of the 5U4 with much less risk.

Dynaco used at least three power transformers in the ST-70, large stack cloth lead, small stack cloth lead and small stack vinyl lead. The small stack transfomers are really compromised as it is. If you want to screw around with additional current draw and have one, it might be a good idea to switch to one of the higher current new transfomers available from Triode Electronics, Dynakitparts or have Heyboer make one up for you.

On page 10 (or 12 of 16 counting the .pdf way)of Hifitime's manual, "The 5U4 or 5U4G can be used in place of the place of the GZ34." Not that everyone here doesn't already know, but the GZ34 is the 5AR4.

Another Dynakit ST70 manual states, "using this tube [5U4G vs 5AR4 - Trelja insertion] type will cut down on the maximum power rating of the amplifier."

As we know, during that era, the goal was to deliver as many watts as possible, and in addition to far better sound, that's what the 5AR4 provides.

I recently finished building a new Stereo 70. It has the new Dynakitparts PT wound for 122VAC line. I put a thermistor in the PT primary and did some other enhancements, but the circuit is still essentially the original.

The amp sounds great. I just got a set of the new Tung Sol 6L6G and have tried them with 5U4GB and 5U4G rectifiers. There was no need to change-out the two 10k resistors in the bias supply. The greater voltage drop of the 5U4 and probably also the 122VAC PT make this possible.

I’ve tried this amp with the 5AR4 with JJ E34L, EH EL34 and JJ KT77. The 5U4/6L6G combination is better than all of them, to my ears.

Regards,
Peter

I have been wanting to follow up on my post above about the 6L6G in my Stereo 70.  Initially I thought it had a very impressive midrange, but as time went on and I tried different 5U4 rectifiers, it became apparent that I wasn't so crazy about it, after all.  It seemed kind of fuzzy or something and the top end didn't sound quite right to me.  Whatever.  I know a lot of folks like 6L6 in the Stereo 70, so to each his own.  My favorite so far is the Gold Lion KT77.  I understand that the EH 6CA7 is probably also a very good choice.  I have reason to believe some Chinese tubes have really good potential in the 70 if you can find them properly screened and with straight pins.

I'm not a fan of 6L6 or 6N3SE in my modded 70. They just sound fuzzy, even the RCAs. It's probably amp and listening preference specific.

My favorite tubes are the Tesla E34L, JJ E34L blue glass and GL KT77s, in that order.

I'm not fond of my welded plate EH 6CA7 either. The cheap Chinese tubes sound good in my amp if money is a consideration.

Ii also have a preference for vintage 5AR4s, but if they are not available the GL is serviceable, nothing more.