Rick J B Posted September 26, 2014 Author Share Posted September 26, 2014 I have to include in a tube rolling thread to keep an eye on bias. If new tubes have the same number and burn in easily then biasing should not be much of an issue. But with a switch even with automatic biasing it is smart to keep an eye on bias to keep the amp safe. ] I have 2 friends that help me keep an eye on the bias on older tube gear as well as new tube gear I have or have had. When switching actual label numbers on a tube re biasing is usually a must. Even if new tubes burn in or the tube swap goes well. Beeker, what about so called "self biasing" amps? My Decware amp is supposed to be set up that way. Quote Link to comment Share on other sites More sharing options...
beeker Posted September 26, 2014 Share Posted September 26, 2014 should be good. I really don't know much other than if the bias is off there will be issues. id read online or check reviews and see if there have been issues with your particular model/amp and its self biasing. I just had to ad keep an eye on bias to a rube rolling thread more for amps with no self biasing in particular even with non automatic biasing amps iv never had bias issues even when switching tube numbers but still keep an eye on it to be safe Quote Link to comment Share on other sites More sharing options...
Audible Nectar Posted September 26, 2014 Share Posted September 26, 2014 (edited) A1's run down, especially his choice of rectifier, jogged my memory and I remembered I had a used GZ34/5 tube stashed. It was made for EICO by Mullard I'm guessing early to mid 60's? Sounds about right. Look at the code on the tube - it will read something like "f32 B2C4". Probably around '62-'66. Sadly while much of the print on this tube is still in good shape, some of it has rubbed off. The only things that are clear are: GZ34/5 EICO by Mullard. Made in Great Britain. ......212. Look more closely where the glass meets the base - there is an acid-etched code on the glass. This doesn't rub off. Would be shocked if it isn't there. AN, here are some photos of the EICO tube. Thats all the info visible on it I'm afraid. Could it be that since it was produced specifically for EICO they left off the etching? Nope. ALL Philips factory tubes of that era have the etching. In your case, it should be just above the top of the black base - near the bottom mica. It might be obscured by the "made in Great Britain" labeling, but that's usually the area it appears. It is small, and even at times will be faint/slight, but will be there. Since we have a picture, though, I can tell that it's a Mullard known in the hobby as a "fatbase", made from 1959-'61 typically, and in the Blackburn factory. Definitely a good one - while all Mullard 5AR4s are really good rectifiers, the earliest are the best. The only older version of the old Philips/Mullard types would be the metalbase - very expensive when you find them. I have a nice little stash of various Philips/Mullard types in house, including a few of the fatbase variety. Edited September 26, 2014 by Audible Nectar 1 Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted September 27, 2014 Share Posted September 27, 2014 I have to include in a tube rolling thread to keep an eye on bias. If new tubes have the same number and burn in easily then biasing should not be much of an issue. But with a switch even with automatic biasing it is smart to keep an eye on bias to keep the amp safe. ] I have 2 friends that help me keep an eye on the bias on older tube gear as well as new tube gear I have or have had. When switching actual label numbers on a tube re biasing is usually a must. Even if new tubes burn in or the tube swap goes well. Beeker, what about so called "self biasing" amps? My Decware amp is supposed to be set up that way. Rick, the nice thing about self biasing amps is that they are truly "plug and play." There's often quite a bit of production tolerance variation among even identical tubes which causes them to draw more or less current. With self biasing, the tube will adjust its own parameters accordingly to establish the needed operating point. The nice thing about single ended tube amps is that they can sound wonderful even when those operating conditions are varied over a fairly wide range which is why, with some amps, so many different tubes can be used which makes it a simple matter for the listener to go with those which are most pleasing. Maynard 1 Quote Link to comment Share on other sites More sharing options...
Rjk1972 Posted April 20, 2016 Share Posted April 20, 2016 I've got my Fisher 500c off at NOS Valves for a work over. I retubed it with all NOS tubes from Brent Jesse and Viva Tubes (for the small signal tubes). TungSol 12ax7 Blackplates in the phase inverter, Matsushita 12ax7s in phono and tone spots and 3 Sylvania 12ax7s in MPX. The small signal tubes are all NOS TungSol with one Mullard for the 6ha5 and one RCA for the 6hr6. I also have some Ratheon and Sylvania Blackplates and recently picked up a pair of Sylvania Gold Label JHS 5751 tubes for the tone spots to cool off my Rega DAC-r's output a bit. I'm gonna go for a matched quad of the new TungSol 7591s. I've read through this thread and am wondering if anyone has any new suggestions or new favorite tubes? Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted April 20, 2016 Share Posted April 20, 2016 Just wondering what your logic was in choosing which tubes (manufacturers/construction) to put in specific locations? Obviously you've given this quite a bit of thought, and I'm just curious Again, not a critique at all, just curiosity. Thanks! 1 Quote Link to comment Share on other sites More sharing options...
Rjk1972 Posted April 21, 2016 Share Posted April 21, 2016 Well when i bought her all the 12ax7s were new TungSols and the small signal tubes were on their way out. The TungSol Blackplates are great in demanding applications and sound great and last forever so I figured they were naturals for the phase inverter spots. I wanted good NOS tubes that would perform and last for the MPX that weren't to expensive and I am not a fan of new 12ax7s through experience so that where the 3 Sylvanias came in. I had a pair of 60s Mullards in the phono section but they but one went microphonic and in the tone control I was running a pair of the new TungSol. I had heard the Matsushita tubes were very close to Mullards in sound and that the factory was set up by Mullard so I figured I'd give a couple of pairs a shot as the two matched pairs were 100 bucks delivered. All the small signal tubes were replaced with tubes recommended by the guys over on audiokarma. The Matsushitas sounded ok and I was enjoying them but thinking of switching out to the Raytheon Blackplates for tone and the Sylvania Blackplates in the phono section but then the not so great restoration that was done on the 500c went bad. Started getting a loud "motorboating" sound out of the left channel. I had been thing about sending it in to NOS Valves anyways as it was having little glitches pop up now and then so off she went. I figure I will change the tone and phono tubes out after I get her back. While she has been away I was doing some reading about the benefits of 5751s and their lower gain coming in handy when you are running high output DACs like my Rega. So I figured I would buy a nice pair and try them out. I know Craig from NOS Valves recommends the Teles so I figure this summer I will try a pair. Quote Link to comment Share on other sites More sharing options...
Rjk1972 Posted April 21, 2016 Share Posted April 21, 2016 Oh and I have always like the sound of the Raytheon and Sylvania Blackplates. Rich like the RCA Blackplates but with a cleaner more detailed sound. Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted April 21, 2016 Share Posted April 21, 2016 Great, thanks for all of that information. It's always nice to read others experiences and opinions on these types of issues. Quote Link to comment Share on other sites More sharing options...
Rjk1972 Posted April 21, 2016 Share Posted April 21, 2016 Great, thanks for all of that information. It's always nice to read others experiences and opinions on these types of issues. Can I ask what you use? I'm trying to get some ideas for different tubes to roll. Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted April 21, 2016 Share Posted April 21, 2016 Nothing really all that much different from what you've been trying. I've been very happy with the RCA blackplates, Sylvania's, and Tele. I'm trying to simplify my amps and preamp configurations, and don't roll tubes anymore. Glad you are having fun with it! Quote Link to comment Share on other sites More sharing options...
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