Sweet...

[groovtubin]

What would be the value/wattage of the resistor for the RF mod?

thanks

[tonelab2]

Thanks groovtubin.
What wattage would be best or to put it another way, how many charlies?
thanks again

[pedro]

groovtubin

where do you get the 78Ohm value from for the 50watter - I have used a 500Ohm - is this overkill ?

cheers
Pete

[tonelab2]

I think I'll use a 25watt, should be enough.
Where the 78ohm measurement came from I've got no idea.

[groovtubin]

Thanks groovtubin.
What wattage would be best or to put it another way, how many charlies?
thanks again

[groovtubin]

groovtubin

where do you get the 78Ohm value from for the 50watter - I have used a 500Ohm - is this overkill ?

cheers
Pete

[Robert]

I've used both a 500Ohm 25 watt and more recently a 1KOhm 10 watt due to something I read somewhere about changing the feel of the amp. I need to A/B them to see if there is any difference.

[dogears]

Jim,

You are sure shooting from the hip with your size recommendations. The choke replacement resistor needs to be sized large enough to allow the screens to sag a bit. The 50 watter should get a larger resistor than the 100 watter due to the screen demands. If you use to small of a resistor you will not get the full effect of the screen sag.

I like 250ohm to 500ohm depending on amp wattage. I also like a switch to go between the choke and resistor. If the choke is roughly 100ohms then the resistor should be a bit bigger so there is a noticeable change when switched.

You don't need 25 watt resistors... Way overkill. Mouser has nice cement 5 or 10 watters that work just fine.

[pedro]

thank you learned friend

Ive used 2 x cement 1K 5w in parallel.

I have a spare partidge choke and hammond choke so when amp is finished I will try all 3 and report back.

cheers
pete

[Robert]

I have now A/B'd 250ohm and 500 ohm resistors instead of a choke. The 500 ohm responds more quickly and the 250 slower, i.e. with increased sag. It will be interesting to try lower and see where the optimum point is. I preferred the 250.

[tonelab2]

Thanks groovtubin, Thanks dogears.

I recall seeing a chassis shot of a dumble many years ago with a 10watt sandstone resistor near the P.T. ( didn't know what it was for), which leads to my next question.
To make this switchable (choke/resistor) what size switch is required?
Is it safe to use a 120v-6amp(240v-3amp) ect.? Are switches subject to Ohms law?

[mlp-mx6]

I have now A/B'd 250ohm and 500 ohm resistors instead of a choke. The 500 ohm responds more quickly and the 250 slower, i.e. with increased sag.

Not to contradict you, but this does not make sense to me. Logically the higher resistance would lead to more sag. Are you SURE about this?

[groovtubin]

Jim,

You are sure shooting from the hip with your size recommendations. The choke replacement resistor needs to be sized large enough to allow the screens to sag a bit. The 50 watter should get a larger resistor than the 100 watter due to the screen demands. If you use to small of a resistor you will not get the full effect of the screen sag.

I like 250ohm to 500ohm depending on amp wattage. I also like a switch to go between the choke and resistor. If the choke is roughly 100ohms then the resistor should be a bit bigger so there is a noticeable change when switched.

You don't need 25 watt resistors... Way overkill. Mouser has nice cement 5 or 10 watters that work just fine.

[dogears]

Agree with Pedro. Big ohm = more sag

I have now A/B'd 250ohm and 500 ohm resistors instead of a choke. The 500 ohm responds more quickly and the 250 slower, i.e. with increased sag.

Not to contradict you, but this does not make sense to me. Logically the higher resistance would lead to more sag. Are you SURE about this?

[dogears]

That's me... LOL!

Jim,

You are sure shooting from the hip with your size recommendations. The choke replacement resistor needs to be sized large enough to allow the screens to sag a bit. The 50 watter should get a larger resistor than the 100 watter due to the screen demands. If you use to small of a resistor you will not get the full effect of the screen sag.

I like 250ohm to 500ohm depending on amp wattage. I also like a switch to go between the choke and resistor. If the choke is roughly 100ohms then the resistor should be a bit bigger so there is a noticeable change when switched.

You don't need 25 watt resistors... Way overkill. Mouser has nice cement 5 or 10 watters that work just fine.

Ah yeah you are right dogears, i`ve tried it alot of ways, just pefered that to the larger values. I was looking for just a HINT of sag. As with all this stuff, there really is no wrong or right, just what feels good to YOU!! LOL!!
peace, jim ah, i know who you are now! LOL! Great ta hear from you!