|Myring Wiring - Making the World Sound Better
(some of us have real work to do, including Avalon Design repairs).
A note about tubes for the VT-Series
I don't sell the 6922EH tubes used in the VT-737sp and VT-747sp. If you want to try replacing tubes yourself, they are retail items which you can buy in sets from Sweetwater or your local distributor.
I supply and fit tubes only as part of a repair when I can test them and burn them in. If you think it is too much trouble and too expensive to send your VT-Series for test and repair, bear in mind that you may save the cost of a set of tubes if your problem turns out not to be tube-related. If it is, I only replace the tubes that are necessary to return to specification, another potential saving.
An interesting aside:
I recently serviced a pair of very early VT-737 (with purple knobs). Older readers will recall that very early units were fitted with elapsed time counters that go up to 99,999 hours and in this pair, they were up to approximately 75,000 hours. Still on the factory original tubes at the previous service, this time round I needed to change only one out of the eight to restore performance - even that was marginal.
Customers have been tempted to buy exotic variants of the 6922 from online suppliers. These tubes may have a claim of being tested on one of the popular tube testers, or they may have been cryogenically treated, or subjected to some other enhancement, but these procedures do not always reveal excessive noise, microphonics and distortion. These parameters can only be assessed in the intended application. I have not seen a recent ST-4 6922EH set, or tried to buy one, so I can't comment on the quality or availability of the tubes currently on offer.
To illustrate this, I note that two VT-747sp recently repaired had been fitted with some 'unofficial' tubes. In one case there was a crackle; in the other, two of the tubes were microphonic and rang like a bell. Another customer bought a set of 'cryogenic' tubes for his VT-737sp and then complained of excessive hiss, believing it could not possibly be the tubes because they were new. I suggested he revert to the tube set I had provided, and which I had carefully tested and auditioned. Then it was fine.
Details of all products, and some handy trouble-shooting hints can be found on the Avalon Design website.