grafting in a 5G9 tremolo

[andrew]

I have an amp with a TW Express bias circuit and I want to graft in a Fender 5g9 tremolo circuit. http://www.freeinfosociety.com/electron ... php?id=807 The Fender has no bias pot.
One intensity lug goes to the 1 meg- the center lug goes to the two 220K bias resistors. I'm not sure where the third lug would connect to the bias supply on an Express bias circuit. Thank you for any help.

[Phil_S]

...to the bias supply takeoff point, between the 15K and 47K, at the 2nd 10u cap. Treat the 47K resistor + 25K pot as a single package for this purpose.

[tubeswell]

Replace the 56k resistor in the 5G9 bias circuit with an appropriately sized pot (wired as a variable resistor) and series resistor (to guarantee a minimum bias should the pot wiper fail) - say a 20k-50k pot and a 47k-56k resistor

[martin manning]

Take note of the cathode voltage on the 5G9 schematic- 260V! This is far in excess of the max heater-cathode voltage of some tubes. Typical Vh-k max ratings are from 100-200V.

[tubeswell]

If you find a good enough old tube you can make it work. Otherwise you could use a triode LFO stage followed by a mosfet source follower - I have done this successfully on a few amps to overcome the potential h-k insulation breakdown issue.

[andrew]

Thanks for the help guys I'll see what happens. If I can't get it right is there a 6sj7 trem circuit out there?

[tubeswell]

Here's an example of one of my amp's with a trem circuit with a mosfet source follower buffer stage

[img1191]http://farm9.staticflickr.com/8029/8031 ... 9886_o.jpg[/img][/url]

[martin manning]

...If I can't get it right is there a 6sj7 trem circuit out there?

6SJ7 is a single pentode, so not a very convenient choice. Got a 6SL7 dual triode? It's also an octal, and the attached Ampeg circuit uses it for a bias-varying tremolo. Per another Ampeg schematic the unmarked resistor is 270k.

[andrew]

Martin, I have a 6sl7.How would I attach the intensity pot to the bias resistors and bias supply? Thanks for any help.

[martin manning]

TAG member Hired Hand has done this, but he is having some problems. It was working well and then became intermittent.
https://tubeamparchive.com/viewtopic.ph ... highlight=

Basically, you can model the intensity pot interface after a Fender bias-varying trem such as 6G16.