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Came across this site at vintageamps.com. They are advertising a quad of Mullards EL34's for $175. Is the tube worth it. Also these tubes are used and not new so how would I know if they have much useful life left. Also anyone have any experience with them? Any suggestions would be highly appreciated.Thanks in advance.
Follow Ups:
Not really worth the price, IMO.
A quad of JJ Tesla E34L (two years back, when they were still available) sounded much more extended and balanced in a modified Dynaco ST-70.
I'd save my money (and sanity...) and go with new production tubes.
Serus,What do you bias the JJ E34L to, in the ST-70?
Make sure the tubes were tested with a good quality mutual/transconductance tester such as the UK made AVO VCM 163, German Neuberger 375 or one of the better US Hickok 5xx series, or the like.
Any readings off a simple emission tester are rubbish and totally useless.Get the transconductance reading in either US Gm (micromhos)or European mA/V (milliamps per volt), as well as the corresponding anode/plate current.
I've seen bad tubes that measure well for transconductance and plate current on testers with low plate/screen voltages (i.e. less than 250v as in most Hickok 5xx, 7xx & Funke W19) but glow red or have low plate current readings when subjected to normal operating voltages. The higher the test voltages (250~450v) applied, the better. Unfornately, there are only a few testers that have this capability, the Neuberger 375 and AVO VCM 163 as mentioned by Dieter, and also the Metrix U61 and Neuberger 370.Also, watch out for any visible stains or discoloration on the plate which often are burn marks due to inter-element leakage.
Thank you guys. Those are all good questions that I hadn't thought about. I have sent them an e-mail with those questions and am awaiting their response. I'll keep you all posted with what I hear from them.Thanks again guys.
Mr. Verma,
They are very good tubes.
Ask the seller the following:
1. What are the transconductance values for each tube?
2. What type of tester is he testing on? (hopefully a 539B/C Hickok)and when was the last time it was calibrated (and by who!)?
3. What is the current draw at what plate voltage and what neg grid voltage?
4. What are the Mullard codes etched on the glass?If he can't answer these: pass
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