Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: PharmRock on February 21, 2022, 06:38:31 pm
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I have previously built an amp that had an EF86 but it was a head. I used the little silicone dampener rings and never had any problems with microphonics.
This time I am building a combo amp, and there's several places that talk about doing a shock mount for the EF86 since the tube is only a few inches away from the speaker. Here's a video from several years ago that talks about taming the EF86:
https://youtu.be/z7yHtoxkdb8 (https://youtu.be/z7yHtoxkdb8)
Anyone have any experience with any sort of shock mounting for an EF86 (or any tube for that matter)? If so, please share your approach and whether it was successful or not.
I am debating whether I should pre-emptively shock mount the tube, or just use the silicone dampener ring approach and address any further modifications if needed.
Thanks!
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Ciao PharmRock
(https://i.imgur.com/roM8p8M.jpg)
https://www.langrex.co.uk/products/b9a-mcmurdo-skirted-anti-vibration-new-valve-base-socket-x1pc-b14/ (https://www.langrex.co.uk/products/b9a-mcmurdo-skirted-anti-vibration-new-valve-base-socket-x1pc-b14/)
As far as I can know those rubber socket where sold also as Geloso rubber sockets
One other way, that was used by our friend HotBluePlates on his Standel 25L15
(http://el34world.com/Forum/index.php?action=dlattach;topic=14263.0;attach=34439;image)
(http://el34world.com/Forum/index.php?action=dlattach;topic=14263.0;attach=34441;image)
In an excess of zeal you might think of using both the aluminum plate method in conjunction with rubber cushioned sockets (this because you say the sensible tube is near the speaker)
Franco
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Thanks Franco,
I recall seeing the "floating mounting plate" picture (or something similar) somewhere, but did not realize it was HBP.
As for the shock-mount sockets with the gasket...I may try that approach. I ordered a sheet of 1/8" silicone pad and will try to fabricate something similar. I've also seen a "floating gasket" approach as shown at the bottom of this thread: https://www.trinityamps.com/phpbb/viewtopic.php?f=2&t=1086 (https://www.trinityamps.com/phpbb/viewtopic.php?f=2&t=1086)
Thanks again.
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Fender was using rubber grommets back in the mid '50s...
http://sluckeyamps.com/harvard/h02.jpg
Also, this type of tube shield will help reduce vibrations...
http://sluckeyamps.com/phoenix/p8.jpg
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I made up a Vox AC15 clone in a combo enclosure and used some of the mitigation examples shown in link - https://www.dalmura.com.au/static/Microphonics%20in%20valves.pdf (https://www.dalmura.com.au/static/Microphonics%20in%20valves.pdf).
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I stole a mount from a Voice of Music VM730 tape recorder.
Then I noticed something when scrapping old computers a friend brings by.
A worn out CD rom from a desktop computer has some rubber mounts that isolate the disc transport.
Even laptop cd rom drives have them. Really jiggly little silicone grommets.
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someone on the forum here (Tubenit maybe) made a shock mount from a silicone pot holder thing. I thought that was genius. I have used small rubber grommets and small O-rings. Gibson used something like that in some of their amps.
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I made up a Vox AC15 clone in a combo enclosure and used some of the mitigation examples shown in link - https://www.dalmura.com.au/static/Microphonics%20in%20valves.pdf (https://www.dalmura.com.au/static/Microphonics%20in%20valves.pdf).
Awesome resource...thanks for sharing. Looks like there's more than one way to tackle the problem. I found it interesting that the article allows you to actually quantify how much mass you might need to add to maximize the damping effect of the foam, etc.
Also, this type of tube shield will help reduce vibrations...
http://sluckeyamps.com/phoenix/p8.jpg
I think I've seen this type of shield in a few of your builds. What is different about these vs. the typical spring-loaded metal tube shield? If you could share the supplier info, I sure would appreciate it.
someone on the forum here (Tubenit maybe) made a shock mount from a silicone pot holder thing. I thought that was genius. I have used small rubber grommets and small O-rings. Gibson used something like that in some of their amps.
That is pretty cool....I did order a sheet of 1/8" silicone rubber that looks like it will do the trick for vibration isolation. I also picked up some rubber washers at Lowes, although I think the ID might be a little too large for the #4 screws at the socket base.
Thanks again for all the tips/info
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I just use tiny rubber O-rings from the hardware store. Works great.
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I think I've seen this type of shield in a few of your builds. What is different about these vs. the typical spring-loaded metal tube shield? If you could share the supplier info, I sure would appreciate it.
The IERC shields are more than just a metal shell around the tube. There is a "mesh" structure inside the shell that makes firm contact with the glass. I think the main purpose is heat dissipation, but the compression contact with the glass also helps prevent vibrations. These shields fit so snug that often times when you want to remove the shield you will also remove the tube. Very popular in old military equipment. I salvaged a box full from a decommissioned FAA radar system. I doubt they are still in production, but you can find them at ham fests, some old surplus stores, and of course, on eBay.
https://www.ebay.com/itm/115169888373?hash=item1ad0a90875:g:17oAAOSwhzNh1L0J
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Thanks for the info. There's a ham fest here in Birmingham next weekend. Never been to one but my brother in law (RIP) used to go quite frequently when he was able. I'll see about going and hopefully come away with some good finds.
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Also I've some of those sockets with shield, as Sluckey say, they can be found at HamFest, but not anytime
Franco