thanks Steve!SDM wrote:When you slap 500K's acrossed your 220K bias feed resistors as in a very popular version of the PPIMV your drop their value to 152.8K when the pot is cranked. With a 470K dual pot they drop to about 149.8K, only 3K difference. Either leaves you 70K short of 220K at least.rockstah wrote:it will be 30k away from 500k. when your volume is up full it will have 470k resistence. 30k away from away from being on 10 so to speak.Kuli wrote:Hi guys!
Will one of these pots do the job?
http://elektronik-lavpris.dk/eshop/show ... O_ID=95602
I know it's a 470K pot and the recommended pot is a 500K. What effect will a 470K have compared to a 500K?
The PPIMV (Post-PI-Master-Volume) thread.
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So Idealy you would want to have the resistors & pot = 220K (when pot is wide open) ?
So I would need to play around with the resistor values to get this match.
Does any one know the dirference in Mod I that uses the dule 1meg pot v's ModII
Just hooked up the Mod II on my build (not that impressed)
I did rebias the amp with pot (PIMV master)maxed out (after I installed it) might have to muck around with the fixed resistors (HMM maybe change them with two pots and fine tune it)
The other thing I noticed when turning master down the out put tubes start to glow more on the plates (i take it this is normal)
So I would need to play around with the resistor values to get this match.
Does any one know the dirference in Mod I that uses the dule 1meg pot v's ModII
Just hooked up the Mod II on my build (not that impressed)
I did rebias the amp with pot (PIMV master)maxed out (after I installed it) might have to muck around with the fixed resistors (HMM maybe change them with two pots and fine tune it)
The other thing I noticed when turning master down the out put tubes start to glow more on the plates (i take it this is normal)
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Don't use a dual 100Klin as shown, but a dual 250Kaudio - then put a 2.2M resistor from each wiper to each output (where the bias voltage is supplied), then you avoid tube death after a possible wiper failure.
Larry
Larry
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that will make a loudness jump, but works
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But the 'Trainwreck Pages' from that book.rockstah wrote:"a desktop reference of hip vintage guitar amps" by Gerald Weber. kendrick-amplifiers.com
Larry
The fault almost always is sitting in front of the amp
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yes indeed - it has atranwreck section in the book.novosibir wrote:But the 'Trainwreck Pages' from that book.rockstah wrote:"a desktop reference of hip vintage guitar amps" by Gerald Weber. kendrick-amplifiers.com
Larry
Larry talk to me more about the 250k dual pot and the 2.2m resistors - not sure where they go
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Ok - step by step:rockstah wrote:Larry talk to me more about the 250k dual pot and the 2.2m resistors - not sure where they go
- The coupling caps are connected to the input lug's of the pot
- The bias supply voltage (which usually feeds the both 220K) is connected to the output lug's of the pot (of course to both)
- The pot's wipers are connected to the power tube's grids (or to their swamp resistors)
- Now simply solder each a 2.2M on each section of the pot from the wiper to the output lug - a small 1/4W resistor will do it
These are only for safety, because if the pot's wiper fails, then the output tube's grid is w/o bias voltage and will immediately jump over the Jordan.
But with the resistor applied and a failing wiper, although this side can't be regulated anymore, but nevertheless there's bias voltage on the output's grid - and the tube(s) will survive
Larry
The fault almost always is sitting in front of the amp
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thanks Larry,novosibir wrote:Ok - step by step:rockstah wrote:Larry talk to me more about the 250k dual pot and the 2.2m resistors - not sure where they go
- The coupling caps are connected to the input lug's of the pot
- The bias supply voltage (which usually feeds the both 220K) is connected to the output lug's of the pot (of course to both)
- The pot's wipers are connected to the power tube's grids (or to their swamp resistors)
- Now simply solder each a 2.2M on each section of the pot from the wiper to the output lug - a small 1/4W resistor will do it
These are only for safety, because if the pot's wiper fails, then the output tube's grid is w/o bias voltage and will immediately jump over the Jordan.
But with the resistor applied and a failing wiper, although this side can't be regulated anymore, but nevertheless there's bias voltage on the output's grid - and the tube(s) will survive
Larry
so these resistors will not effect tone? are they not input grid resistors are they? wont this change the pots value?
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NO!rockstah wrote:so these resistors will not effect tone?
If the pot's value is exactly 250K, then dimed it drops to 224.49Krockstah wrote:are they not input grid resistors are they? wont this change the pots value?
Larry
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great! so last the thing is, how did you come to the 2.2M value for the resistors being needed here?novosibir wrote:NO!rockstah wrote:so these resistors will not effect tone?
If the pot's value is exactly 250K, then dimed it drops to 224.49Krockstah wrote:are they not input grid resistors are they? wont this change the pots value?
Larry