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Post by coffeetones on Dec 21, 2013 9:29:25 GMT -7
Hello folks, I just joined the forum - Greetings.
Could anyone definitively inform me about the pitfalls of using EL84 pins 6 and 8 as tie points for screen and grid resistors? I see a lot of mixed information on tube datasheets and in other conversations. Which tubes will and will not allow this?
Thanks
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Post by coffeetones on Dec 29, 2013 18:40:43 GMT -7
Hello?
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Post by randalp3000 on Dec 29, 2013 19:28:16 GMT -7
Well hello new guy, maybe some of these fine folks do not know the answer to the question. However here is something I ran across awhile back which should be helpful taken from www.kcanostubes.com/content/modern-el84-amps-and-nos-el84s. Modern EL84 amps and NOS EL84s There are several modern EL84 amplifiers which have wiring violations on pin 1 of one or more EL84 sockets. NOS EL84s have internal connections between pins 1 and 2 where modern EL84s do not. Sometimes designers of EL84 amps assume that pin one is a safe location for a "tie point", a place to connect a grid resistor and the signal wire from the phase inverter. This will result in a NOS tube placed in such a socket furiously "red plating" and the amp humming. If run this way for long enough, damage to the EL84 tube and/or the component connected to this socket will result. These amps can be modified by disconnecting and moving this junction off of pin 1. Best options and methods will vary from amp to amp with non PC mounted sockets being the easiest to modify. Contact a qualified amp repair technician to do the work. Known amps with this problem: Lexicon Signature 284 Laney VC30 Fryette Memphis 30-Only applies to outer 2 tubes on units with serial numbers (last 4 digits) 0141 or lower. Crate V18 Jackson Ampworks Britain 3.0 and earlier (4.0 is ok) At least one Mesa amp (but definitely not all), which I can't recall,has this situation. No problems with: Bad Cat, Matchless, Dr Z, Fender Blues and Pro Jr, Vox, Gibson Goldtone GA15s, Mesa Lonestars, Kingsley Amps, Jackson Ampworks Britain 4.0 (check with Jackson on his other amps), Seymour Duncan 84-50 and many other amps will work fine with NOS EL84s. |
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Post by bluzman on Dec 29, 2013 19:34:23 GMT -7
I got nuthin' for ya!
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Post by coffeetones on Dec 30, 2013 10:06:47 GMT -7
Is there any way to pull Mike / Dr Z into this conversation? He has at least one amp that uses pins 6 and 8 as tie points for the screen and grid resistors. Surely there must be guidelines for swapping tubes in that amp. Thanks
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Post by Jaguarguy (Mike) on Dec 30, 2013 10:19:16 GMT -7
You can always send a note to Doc or Don asking same question. Just click above Z amps link and send them the question.
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Post by randalp3000 on Dec 30, 2013 12:01:29 GMT -7
I think all my Z amps use 6&8 for jumpers. All the data sheets I just pulled up have no connections on pin 6 or 8 so I wouldn't sweat it, just stay away from pin 1. Personally I like to use a small turret board or terminal strip for grid and screen resistors leaving the extra pins open. like this  or this  all the best rp |
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Post by Albert on Dec 30, 2013 20:08:08 GMT -7
I think all my Z amps use 6&8 for jumpers. All the data sheets I just pulled up have no connections on pin 6 or 8 so I wouldn't sweat it, just stay away from pin 1. Personally I like to use a small turret board or terminal strip for grid and screen resistors leaving the extra pins open. like this or this all the best rp Is this the amp I you tried for me .it waz awsome .. I need to come get that ep boost maybe this week . |
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Post by randalp3000 on Dec 30, 2013 21:19:00 GMT -7
I think all my Z amps use 6&8 for jumpers. All the data sheets I just pulled up have no connections on pin 6 or 8 so I wouldn't sweat it, just stay away from pin 1. Personally I like to use a small turret board or terminal strip for grid and screen resistors leaving the extra pins open. all the best rp Is this the amp I you tried for me .it waz awsome .. I need to come get that ep boost maybe this week . I think that was the amp and give me a heads up if your coming and I'll pull the EP off my board. Look forward to seeing you Albert. |
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Post by coffeetones on Dec 31, 2013 9:37:16 GMT -7
Looking at the pictures, I'd say randalp3000 has "the sickness". LOL
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Post by randalp3000 on Dec 31, 2013 14:08:57 GMT -7
Looking at the pictures, I'd say randalp3000 has "the sickness". LOL Yep |
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