vintageHIWATTconvention.com

Happy New Year all! I have to take my '72 DR-103 in for rebiasing (tubes began glowing red; hasn't had new tubes or bias since purchased around 20 years ago). I had another DR-103 in and had bought a current production set of Mullard repros. According to the tech notes on the receipt, the tubes weren't necessarily the best fit — and given how hot original EL34s were able to run in these Hiwatts vs. what today's tubes can handle, thats understandable. So the question: What are some of the most robust and musical tubes that should be considered for these older DR-103s, and any special instructions as to biasing them properly for maximum effect? Would a quad of TAD EL34B STR 1635 do the trick?

I saw a few suggestions at this link, from 2011: viewtopic.php?f=2&t=1475. Looking to see if EL34s mentioned there are still available, but any updated hints very much appreciated.

Looks like the TAD EL34B STR specs slightly higher on Screen Voltage capacity, but I haven't personally tried them. The budget route would be JJ E34L (not EL34) but you may want to order the Burned-in option to weed out any weaklings.

Dave

The TADs look like a good choice.

TADs do sound good and are as reliable as any modern tubes.
Lots of 1972-1973 DR103's have insufficient bias voltage, you might look into Mark's Bias doubler.

Thank you, gents! Just got my matched quad of TADs; will see what the folks at Triple S say about the bias voltage.

Just heard back from techs. I brought them the set of TAD EL34B STRs. I had neglected to tell them that the 20-year-old Groove Tubes I'd had in the amp were starting to burn orange/red, figuring they would just bias the new set of tubes. They are suggesting that, based on the TAD set I brought them, that they want to do a mod to get the 500 volts going through now down to 250 volts (that was a service person in front of shop, not the tech). Tech I spoke further with said mod would be maybe a couple of IECs to drain resistance. He also said that had I not brought in the TAD set that they would research a set of tubes that would allow them to bias per the Hiwatt spec.

On other Hiwatt heads of mine, I've used JJ Electronics T-E34L-JJ-MQ Vacuum Tube Pentode Matched Quad and a set of Tung-Sols, with these reported specs:

A set of four factory Platinum Matched Tung-Sol EL34B tubes. These are factory matched at real world voltages for current and transconductance. The test results are labelled on each tube box as shown. These are difficult to find at a reasonable price, so this is an opportunity to obtain a world class tube at a price that won't break the bank.

The tubes are burned in for 24 hours, factory matched and then each tube is labelled with its test results.

Comments on the sound quality from the maker: "The Tungsol EL34-B is a higher impedance EL34 tube design with increased touch responsiveness and a unique clipping characteristic with a hint of the 6L6 sound."

These are made in the Xpo-Pul factory (also known as Reflektor) in Saratov, Russia.

They are matched by the factory at 400V plate, 250V screen and -17.52V bias. Insist on factory platinum matched tubes for best performance.

Tech offered to research tubes that would fit as-is without a mod, so I said please do. Will certainly post what they discover. Any thoughts re: that dramatic of a bias mod?

UPDATE: Tech further clarified there was a trim pot installed already (which I do see in gut shots I took a few years back), set perhaps to Mullard strength. They will replace that and try to get the TAD set to run hot as possible w/o blowing.