![[-]](https://theultimatetone.com/images/collapse.png "[-]")
04-25-2023, 07:19 PM
Hi Guys
Drew - All of those ideas can be tried and have been tried by many tinkerers and builders.
First, regarding repurposing the second input jack: The hi/lo jacks on Fenders are fairly redundant now, since every player has his own amp and the low-gain input is also low-z, which is not so great for your guitar tone. All the extra jacks make great spots to add new pots or switches as your mods dictate.
When there is also a separate triode related to each jack, there is a world of change possible by re-ordering the gain stages, ie, place them in series instead of parallel. This is what turns a plexi into an 800. Even for clean playing, excess gain can make the sound more "liquid" and it can feel like the guitar plays itself.
Regarding switching plate / cathode resistances: There will be a DC shift when these paths are interrupted, so you may want to turn a later volume control down before making the switch. Otherwise, you can make the selection "live" with power on. The way to minimise the thump is to always have a high-value R that remains intact as Rk and as Ra, then add Rs in parallel with them. This is "shunt" switching and it is always quieter than series switching.
An alternative is to have many low-value Rs in series, then the switch shunts the sections not needed. Just as above, there is a DC path that remains intact regardless of the net value selected for Rk or Ra.
Note that in general, when you make mods to the amp that effect DC paths the power should be off.
If you make a mod to the bias supply, REMOVE THE POWER TUBES and test that bias voltage appears right at the tube sockets and is of sufficient magnitude to control the tubes. Then turn power off, install tubes and proceed with bias setting.
Have fun
Drew - All of those ideas can be tried and have been tried by many tinkerers and builders.
First, regarding repurposing the second input jack: The hi/lo jacks on Fenders are fairly redundant now, since every player has his own amp and the low-gain input is also low-z, which is not so great for your guitar tone. All the extra jacks make great spots to add new pots or switches as your mods dictate.
When there is also a separate triode related to each jack, there is a world of change possible by re-ordering the gain stages, ie, place them in series instead of parallel. This is what turns a plexi into an 800. Even for clean playing, excess gain can make the sound more "liquid" and it can feel like the guitar plays itself.
Regarding switching plate / cathode resistances: There will be a DC shift when these paths are interrupted, so you may want to turn a later volume control down before making the switch. Otherwise, you can make the selection "live" with power on. The way to minimise the thump is to always have a high-value R that remains intact as Rk and as Ra, then add Rs in parallel with them. This is "shunt" switching and it is always quieter than series switching.
An alternative is to have many low-value Rs in series, then the switch shunts the sections not needed. Just as above, there is a DC path that remains intact regardless of the net value selected for Rk or Ra.
Note that in general, when you make mods to the amp that effect DC paths the power should be off.
If you make a mod to the bias supply, REMOVE THE POWER TUBES and test that bias voltage appears right at the tube sockets and is of sufficient magnitude to control the tubes. Then turn power off, install tubes and proceed with bias setting.
Have fun
