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PostPosted: Fri Dec 21, 2018 6:07 pm 
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Experienced
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Joined: Wed Sep 12, 2018 5:17 pm
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Location: Shawnee, OK
Completed install of VRM in Trinity Tweed and there was a lot more hiss (at high volume and when the tone control is turned up) :bugeye: than before (some, but not objectionable) :) . VRM was installed per layout with 1M resistors on pin 2 and 7 of V1. Also there is a 1M resistor on each of the inputs per layout. Sooo, 1) Are the 1M's necessary/required in both positions (inputs and V1)? 2) What do the 1M's do on V1?

Also read in documentation that replacing carbon comp resistors w/ Metal Film will help tame the hiss. I don't want to go overboard with the MF resistors. Should I replace the 820R cathode(?) or the 2 100K plate(?) resistors or all three? And will Carbon Film's do the trick (have those in 100K; the 820R will need to be ordered if needed)?

Thanks for any additional information provided.

Edit: Reread the VRM docs and it answered most questions. The 8-16 uF 450V capacitor is added between HVIN terminal and power ground, this is correct? And regarding the resistors to the plate, good/bad idea? :hmmm:

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PostPosted: Wed Jan 02, 2019 1:18 pm 
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Friend
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My install was on a TC-15 so maybe different but...
I did take the resistors off of the input jacks.
My instructions said something like "move the 1M resistors from the input jacks to the grid."
And I do believe Stephen said something to me about a hum if you don't make this move
So I don't have the 1M resistors in both places.


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PostPosted: Wed Jan 02, 2019 11:35 pm 
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Location: Shawnee, OK
Thanks for the reply! PS Were you on the AX84 forums? I joined AX84 ,but haven't kept up for about 10 years. Work interfered, but retired now. Back to fun!

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PostPosted: Thu Jan 03, 2019 3:21 pm 
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Holy Ghost
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Location: Brighton, Canada
1M should be on the tube if you have a VRM installed. Not in both places.

Read the section called "Introduction to Vacuum Tubes and Common Terms" in our manual. It will tell you what the resistors do.

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PostPosted: Thu Jan 03, 2019 6:28 pm 
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Joined: Wed Sep 12, 2018 5:17 pm
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Location: Shawnee, OK
Stephen, thanks for the definitive reply on my VRM question! I built the Tweed first and added the VRM after the Tweed was running and playing REALLY well. Will make a note in build docs so I won't repeat this mistake again.

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