Members alsendk1 Posted October 29, 2015 Members Share Posted October 29, 2015 I own a Vox V15 combo, and I wonder why one of the valves ECC81 are covered with a metal cylinder. Is there a clever explanation for this? It is the valve closest to the choker at left that is covered...just not on this picture Link to comment Share on other sites More sharing options...
Members Mr.Grumpy Posted October 29, 2015 Members Share Posted October 29, 2015 They're for electrostatic shielding. It helps prevent the tube(s) from picking up hum. Link to comment Share on other sites More sharing options...
Members alsendk1 Posted October 29, 2015 Author Members Share Posted October 29, 2015 Thanks a lot Grumpy ) Link to comment Share on other sites More sharing options...
Members 1001gear Posted October 30, 2015 Members Share Posted October 30, 2015 Vibration too as far as I can tell. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted October 30, 2015 Members Share Posted October 30, 2015 They are often spring loaded to keep the tube pressed into the socket and minimize vibration. They also protect the tubes from being damaged or pulled out when you store cords and such in back of a head or combo and of course the additional shielding for EMF as MR Grumpy mentions. Link to comment Share on other sites More sharing options...
Members Tom Mc1 Posted October 30, 2015 Members Share Posted October 30, 2015 I've always wondered about that. I've only found it on my 12AX7 tubes. It would seem like they want the tubes to get hotter. Link to comment Share on other sites More sharing options...
Members alsendk1 Posted October 31, 2015 Author Members Share Posted October 31, 2015 That`s exactly what`s made me wonder in the first place, Tom!! Link to comment Share on other sites More sharing options...
Members WRGKMC Posted October 31, 2015 Members Share Posted October 31, 2015 The tubes can easily handle the heat. Plus they use convection to cool them (as does the entire chassis) Heat rises drawing in cool air in from the bottom like a chimney stack. The hole at the top (if the tubes mounted vertically) vents the heat. If the tubes mounted upside down, its an inlet for cool air and the heat escapes at the base of the socket They aren't the only type of tube holders. Some amps use springs and clamps on both preamp and power tubes. The "Cans" or Tube Caddy's as they are called in the business prevent hum from the large transformers usually mounted close by. Some amps have the preamp tubes placed farther away from the transformers and have the tubes mounted vertically and do without the cans. You find them in many Hi Fi amps where you have a wide and deep chassis. The tubes are farther away from the Power Supply. In a narrow combo chassis the heads are often mounted upside down and between the gravity, speaker vibration, and moving the amp gig to gig, the tubes are much more likely to fall out. The clips on the pins are much smaller and grip less. Power tubes pin clips are much stronger, plus the "Key" in the center prevents them from being tilter over sideways when they are bumped. Power tubes usually have claws on the side of the base which grasps the base of the tube to hold them in securely. Link to comment Share on other sites More sharing options...
Members alsendk1 Posted October 31, 2015 Author Members Share Posted October 31, 2015 A fine and insightful explanation..thanks! Link to comment Share on other sites More sharing options...
Phil O'Keefe Posted November 4, 2015 Share Posted November 4, 2015 Yup - they're for shielding the high-gain preamp tubes, and they also serve to hold them in place so they don't vibrate out. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted November 5, 2015 Members Share Posted November 5, 2015 I've run my old Bassman head with the covers off and honestly couldn't hear any great increase in hum or noise. It runs clean sound so the tubes aren't gained up very high. It wasn't being exposed to a noisy environment either. In other situations where you may have light dimmers or CRT screens it might be a whole different story. On the other hand, I have an old Sound City amp that gets a whole lot more noise due to its higher gain and chassis design. That ones noisy enough with the covers on. Other amps that overdrive tubes would be much more susceptible to EMF. I'm they can be affected at different levels based on their layout and gain staging. There are many amps that don't use cans, just springs and keepers. Allot of that has to do with running the right version of preamp tube. Some can have better filament voltage shielding, Long tail vs short tail and all of that combined with good hum cancellation can make the cans unnecessary. I still like then for their physical protection. The only thing that might be better were the older military tubes sealed in a black metal can instead of a glass tube. If course you could so without tubes all together and replace them with Solid State replicas. http://eshop.amtelectronics.com/accessories/12ax7ws-warmstone-12ax7-tubes-solid-state-equivalents.html Link to comment Share on other sites More sharing options...
Members onelife Posted November 5, 2015 Members Share Posted November 5, 2015 If course you could so without tubes all together and replace them with Solid State replicas. http://eshop.amtelectronics.com/accessories/12ax7ws-warmstone-12ax7-tubes-solid-state-equivalents.html I'm really interested in checking those out. Do you have any info or experience with them? Link to comment Share on other sites More sharing options...
Members WRGKMC Posted November 6, 2015 Members Share Posted November 6, 2015 No not at all. I just stumbled over them while looking for the metal can tubes. http://amtelectronics.com/products/w...e-equivalents/ I believe they have/had the 12AX7, 6L6 and WL34 types of replacements available. I'm sure the idea of SS replacements for tubes would be considered sacrilegious to most tube lovers. There can be situations where they might make sense, especially if they work as well as they claim. I have an older Hybrid Music Man 65 head. Its front end is all SS and it uses a 12ax7 Inverter and power tubes. They converted those amps later in production when they found the inverter tube could short and cause the head to flame out. I've always kept a new tube in that head just to avoid that problem from ever occurring but a SS replacement would be a permanent fix. The inverted really doesn't add anything to the tone and it would put the safety issue to rest. The specs on the device (wont call it a tube) are very good. It will work in all amps so long as its not a low voltage starved circuit design. Other situations where it may be useful might be in an amp like my Bassman where the bass channel was never very clean. a fuzzy bass tone may be good is some situations but a really clean and solid preamp can make bass sound allot tighter. Having one or a pair as a troubleshooting tool is another. Its easy to find bad tubes by swapping them out. Its not easy to judge weak tubes or tubes with low output. The SS volume, tone and clarity wont change. If you use them as a benchmark when trying out other tubes, you'll know how those tubes stack up. You can spot how much the tubes have aged and how much distortion they are producing. Who knows you may even like them more then normal preamp tubes and prefer a hybrid over a full tube amp. At the moment they seem to be out of stock. Its a Russian build apparently. http://eshop.amtelectronics.com/accessories/12ax7ws-warmstone-12ax7-tubes-solid-state-equivalents.html Link to comment Share on other sites More sharing options...
Members 1001gear Posted November 6, 2015 Members Share Posted November 6, 2015 There's this stuff as well. http://www.robertsaudiotech.com/designs/retrovalve.php Link to comment Share on other sites More sharing options...
Members WRGKMC Posted November 6, 2015 Members Share Posted November 6, 2015 Hadn't seen those. Look like they're half the price too. I may give one a whirl and see what they sound like. Link to comment Share on other sites More sharing options...
Members 1001gear Posted November 6, 2015 Members Share Posted November 6, 2015 The Youtubes suggests they sound a hair less "there" than real in the driven zones. Can't tell much about clean dynamics.and dynamics in general. Link to comment Share on other sites More sharing options...
Members WRGKMC Posted November 6, 2015 Members Share Posted November 6, 2015 You tube is a low quality audio format so I find it hard to trust anything posted for making any kind of audio decisions. All you can say is one may be different then another in an AB comparison. Plus you have to question the mic sensitivity, recording chain, mixing and all of that which can alter the sound or fail to capture it. Many video recorders have AGC on the mics which compresses the signal too to maintain volume levels. If there's an increase in midrange for example, the bass and treble can diminish because the AGC will attempt to keep the DB level the same. Add to that many cameras are only 12 bit audio or less which isn't the best. Unless you're dealing with a high end camera (and techs) and higher sample rates, Its hard to know whether the gear is the issue or the recording medium. I'll likely give it a listen on my studio monitors and see if I can discern some kind of difference. Drive differences should be detectable at least. Link to comment Share on other sites More sharing options...
Members onelife Posted November 6, 2015 Members Share Posted November 6, 2015 I'm sure the idea of SS replacements for tubes would be considered sacrilegious to most tube lovers. There can be situations where they might make sense' date=' especially if they work as well as they claim.[/quote'] If it sounds good then it is good. I used a Fender Montreaux for a while and it was great - 100 Watt two channel solid state amp with MOSFET circuit for overdrive - so I know it can be done in a way that works for me. In fact, my main amp is a Yamaha DG80, which has all the advantages of tubes without the fragility and associated hassle. Link to comment Share on other sites More sharing options...
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