------------------------------ From: chowkwan@alumni.cco.caltech.edu (Raymond Maihin Chowkwanyun) Subject: Re: VTL 225 Date: 2 Jun 93 16:31:30 In article <1ui7hjINNn1s@uwm.edu> cthtan@v9000.ntu.ac.sg writes: I would be most grateful if someone can advise me or give some suggestion on the use of my power amp. It is a VTL 225 fitted with EL34 tubes and my ^^^^^^^^^^^^^^^^^^^^^^^ I wouldn't touch this with a 10 foot pole. questions are as follows: 1) What are the signs and symptons when any of the tubes start to deteriorate? VTL amps don't like DC input. This is easy to check with a multimeter on the output of your pre-amp. As long as you steer clear of DC the power tubes (EL34) will last thousands of hours. More problematical are the input tubes. If you hear a rustling sound, you might try swapping the input tubes between your 225's. If the rustling sound moves, it's time to get some new input tubes (which take a *long* time to break in so don't be surprised if the amp sounds a bit hard at first). 2) What brand of tube is recommended? (I was told that Golden Dragon tubes sound great.) Stick to Tesla EL 34's from VTL is my advice. I switched from GE's to Teslas and there was more harmonic detail and added weight to all instruments. Teslas do take some time to break in. Golden Dragons are made in China and Chinese tubes have a decidedly mixed reputation. 3) What is the optimal bias setting for a good balance of sonic quality and tube life span? ( The factory recommended 275 mV for extended life span of the tubes) Again, factory knows best. Upping the bias to say, 320 mV, may produce a surprisingly beefy sound. Kind of like a tube steroid but your tube life will be reduced. How much? I don't think anyone has a done a definitive study. Even at 320 mV, the tube will be operating way below its rated capacity. 4) Is it true that the use of MIT caps will greatly improve the sonic performance of the amp? This is getting repetitive but why not ask the factory i.e. Luke Manley. He's a friendly guy and always glad to help. Of course, you know that the voltages inside a tube amp can be lethal? Also, MIT may not make caps big enough for your needs. I do know the Manley's hold MIT's in high regard. However, if you start modifying you may void the warranty so check before you do anything. Since you're into tweaks, let me throw out a couple of suggestions: 1) Consider getting VTL to switch your amp over to triode operation. This will likely halve your power output but studies have shown that 99.9% of people who have experienced triode power never go back to pentode (your current mode of operation). The only reason not to do this is if your speakers need the full power of pentode mode. The improvement wrought by triode mode will far outweigh any cap differences, I promise you. It may be possible to install a switch so you can switch between triode and pentode modes. Many of the current VTL amps have this feature. 2) Replace the Belden power cord supplied by VTL with NBS power cord or cord of your choice. You will find the sound seems to "open up". 3) If you get the urge to pour Tweak into your tube sockets, lie down, count to 1000 slowly and then throw that bottle of Tweak away. Tweak deteriorates over time into a white gooey substance that resists electrical current and is hell on earth to clean up. I would also look with a jaundiced eye on tube collars and other such valve prophylactics. -- ray ------------------------------ From: davidj@rahul.net (David Josephson) Subject: Re: VTL 225 Date: Thu, 3 Jun 1993 04:36:49 GMT In <1ui7hjINNn1s@uwm.edu> cthtan@v9000.ntu.ac.sg writes: >I would be most grateful if someone can advise me or give some suggestion on >the use of my power amp. It is a VTL 225 fitted with EL34 tubes and my >questions are as follows: >1) What are the signs and symptons when any of the tubes start to deteriorate? Lower gain, higher distortion, lower overload point. >2) What brand of tube is recommended? (I was told that Golden Dragon tubes >sound great.) VTL's own, generally. Golden Dragon not so great and may fail prematurely. VTL's probably not any more expensive, their EL34's probablu from Tesla rather than Shuguang (Golden Dragon). >3) What is the optimal bias setting for a good balance of sonic quality and >tube life span? ( The factory recommended 275 mV for extended life span of the >tubes) Manley knows what he is doing, leave at 275 mV if it says that. Running more bias current will bring the tubes closer to class A but they are already near their limit anyway. >4) Is it true that the use of MIT caps will greatly improve the sonic >performance of the amp? Improve, yes. Greatly, no, imho. >Thanks in advance. -- David Josephson ------------------------------ From: Andy Moss Date: Fri, 4 Jun 1993 20:00:00 -0400 Subject: vtl 225 Who was it that said?: UGp 1) What are the signs and symptons when any of the tubes start to deteriorate? How about: They go black inside; they sound terrible; they take forever to warm up; one channel sounds different than the other; they rattle when you shake them; they don't glow at all; strange colored things appear inside them when they are on; etc. etc. etc. UGp 2) What brand of tube is recommended? (I was told that Golden Dragon tubes UGp sound great.) I have Mullard EL-34s in my Dynaco and they sound pretty good. I'm going to be trying Siemens tubes next as I have heard good things about them. I hear that the Westinghouse & Sylvania ones sound good too. The Golden Aero tubes cost a king's ransom but I don't know if they sound any better UGp 3) What is the optimal bias setting for a good balance of sonic quality and UGp tube life span? ( The factory recommended 275 mV for extended life span of the UGp tubes) This I don't know. I have always set mine well into the linear range. I can't see it making a big difference in the long run unless you over-bias the tubes. Which is really silly because you kiss goodbye your dynamic range and make the whole amplifier work harder than necessary. If you want to be really critical you can hook the amplifier up to a sweep generator and oscilloscope to set for optimum. UGp 4) Is it true that the use of MIT caps will greatly improve the sonic UGp performance of the amp? Good question! The answer is, "How much money do you have?!". Correct me if I'm wrong, but MIT claims that their cap's have a higher Q and less incidental inductance from foil types. In my opinion, only the most taudry capacitors have enough incidental inductance to be a concern. If you like you can take the capacitor you need and instead use two cap's of half the value in parallel if you insist on reducing inductance. UGp Thanks in advance. Not necessary! Andy --- ~ Magical Mail ~ --