Tubes...Tubes...Tubes :)

Ok so now that my amp is singing nicely, I only have a few odds and ends to tie up...

1) Install the Varistor on the power line (Have a 3 lug terminal block on order to make this neat and proper!)
2) Clean up a few solder joints that I am not happy with (Ran out of solder wick, more on order )
3) 90% alcohol to the board to remove rosin residue
4) Replace the bungled tube socket for the one of the output bulbs that I screwed up (Result of a loose nut between the soldering iron and Chair Too much solder on a pin leaked into the tube socket itself, I can put the tube in and it's tight but it sits 1/8 inch off the bottom and I don't like that look)
5) Some minor wire tidying


So once that is all done (should be this week) I want to start experimenting with some tubes

I have the chineese rectifier that came with the kit and it works fine but I am reading how some Mullards can improve the sound, but I am confused as to what they all are..

From my documentation, this Amp uses a GZ34/5AR4 Rectifier, yet I see people using GZ33 and GZ37's,,, not sure what the differences are....

Also, I am looking at either a pair of KT88 or KT120, but it seems that there are so many to choose from and some are good in one amp and some in another.... I have the Sovtek 6550's right now, but what do you all recommend for a VTa120?


Thanks in advance!

If you have done the infamous "yellow-sheet mod" I wouldn't worry about your rectifier tube first. The differences in sound are subtle and related to voltage-drop. The main reason folks go for the old Mullards is reliability.
Your first priority for sound-shaping should be your center driver tube. There is a wide range of choice here. And no consensus, which is logical because the "best" sound is dependent upon so many factors - speakers, room, sources, yer ears - that one must forge one's own blade, so to speak. Search the forum to be boggled at the sheer range.
Output tubes might be considered second priority. Again, we have a moot. Which means there is no final reckoning. From my own experience, The Man for this is Jim McShane, who not only is an honest dealer, but he puts every tube through its paces and will make good on any failures in a timely fashion.
Some of us have found the latest Chinese KT-88s to be super, but just as many have reported disappointment. Probably not the best place to start, though I'd not rule them out in the future.
In the end, do as I say and not as I did, which was to plunge headfirst into tube-rolling. Get your room set-up in order, and perhaps spring for the SP-14 and then you'll have an even larger set of variables - it never ends.

I would be skeptical of the Chinese 5AR4. Would I spend *that* much for an OE GZ37? Probably not, given my supply of GE 5AR4s.

As to tube-rolling - one piece of advice first: Live with the amp, stock/as-is for a few hundred hours - say 3-4 months. This both burns in the tubes and burns in your ears under a lot of different conditions.

Meanwhile put yourself in harm's way in your search for alternate tubes. Kutztown is coming up in May, and from Jersey City, less than two hours dead-west off I78 (1 hour, 46 minutes, 104 miles). You will be able to collect half-a-dozen options there for less than the cost of a single Russian matched pair of anything. There are other flea/hamfests in-around your area as well.

If you do go, look for me a the club table - I run a diagnostic and repair clinic for vintage equipment, and will be there with various tools and such for the purpose.

Kutztown? is this a Hamfest?

mcgyver74 wrote:Kutztown? is this a Hamfest?  

This is, by any measure, the largest gathering of vintage radio collectors, vendors and similar in the US, probably in the world, at one place and at one time.

http://hagstar.phanfare.com/14281203

This year, it is May 11/12/13, with May 12 being the 'heaviest' day. Most years, there is a fairly large inclusion of vintage audio and more. Thousands of tubes for sale, as well.

As the owner of an ST-120 for three trouble free years I would live with the stock configuration and supplied tubes for at least 500 hours of operation before going down the tube rolling road figure out what you like and dislike about the sound produced with your configuration, speakers and room then you can seek more specific suggestions that will help guide you in the right direction.
Enjoy!

Quick "amen" to Kentley, Peter W and Maintarget, having also learned the hard way. There's no way you can conduct a meaningful 10-hour "test" on any component, or a billion-hour test if you're multiplying variables at the same time.
Good caps take >50 hours to bloom, output tubes at least 100, and signal tubes somewhere in between, maybe. Get fully used to what you're listening to, which takes months and will change as caps form up and tubes settle in. Only when the dust has fully settled can a meaningful comparison be made. As signal tubes have, IMHO, the greatest influence on sound flavour, start there but give them a few months before heading to the altar. For outputs, consider trying used tubes with some life left in them from a reliable source to avoid the 100-hour break-in agonies. Your sockets will thank you.

Thanks guys
After discussing with Jim McShane, as y'all suggested I opted to leave my outputs alone and leave 2 out of the 3 signal tubes alone. HE did recommend that for the center position I upgrade to a 12BH7 (2 of my 3 signal tubes are the same and one is not already) as it gives better performance and since i am breaking in and it's under 20 bucks for a Sylvania I figured what the heck.

For the rectifier I ordered a Genelex GZ34

Should sound great!!!