martin manning wrote:You only need one rectifier and reservoir cap but you need to duplicate the entire divider for each bias sulply. The cap to ground from each supply is there so that both tubes see the same resistance to AC ground. i.e. the 220k bias feed.
10-4 Martin.
Thanks for clarifying that, and of course, for all your help.
best
OK, so I built the dual bias circuit as Martin suggested.
How do I marry that to the bias circuit in the schem above.? Normally I would just run a wire from each bias pot to each 220k resistor. But now, with this bias vary trem, do I need to go through the trem pot somehow.?
Will the trmolo circuit still work as drawn, with a fixed bias in place of the Cat Bias.?
Thank You
Connect each bias circuit to a 220k bias feed resistor, and From the wiper of the trem pot run a 0.1uF cap to each 220k bias feed. You want to impose the same AC voltage from the oscillator on top of the separate bias voltages.
HH, hold on- you'll have to have some resistance between the trem signal and the 10uf electrolytics in the bias supplies, otherwise it will be grounded out. Try two 150k's or 220k's in series for each bias feed, and put the trem signal at the juction. You also will probably have to adjust the fixed resistor above the trem pot to get the tremolo depth dialed in. The peak-to-peak needs to be about equal to the bias voltage.
Hey Martin -
I really appreciate your efforts here.
Just to clarify, are you saying:
Instead of ONE 220k resistor for each bias feed (from each bias pot).
Use TWO of that value, and join the trem signal (from the wiper of the Intensity pot) at the junction of those 220k.?
Sorry, this gets confusing.
I may have out-smarted myself with this dual bias idea.
Thank You
Last edited by C Moore on Tue Jul 03, 2012 1:05 pm, edited 1 time in total.
Yes, two 150 to 220k in series for the bias feed from each of the dual bias supplies, and then bring the trem signal from the trem pot wiper through two 0.1uF caps, one to each bias feed's center junction.
Using a dual pot for the intensity control would reduce the parts count if you have one, I think I'd use a 250k. Then you could just run one 220k bias feed from each wiper, and connect the bottom (CCW lug) of each pot to the separate bias supplies.
Yeah, I already have Space/Lay-Out issues. Every time I try to Convert/Re-Purpose one of these old pieces of gear, I get in over my head. It is hard for me to foresee all the troubles coming down the road.
Plus, it is hard (is for me anyway) to build on a "square" chassis. Everything gets bunched together. I also am forced to use both sides of the chassis, and then I end up with what looks like a "First Time" build... if you know what I mean. Things just kind of look a mess.
Partly my fault no doubt, but a guy is kind of forced to put things where ever you can.
Anyway..... let me think about this dual pot vs the series resistor options you mentioned.
Thank You So Much
Neatly done, but you are indeed running out of room! I think with the dual pot you still want to isolate the two halves, so you'd want to have two identical networks comming off of the trem output tube's plate: cap, resistor, pot. The difference in parts count isn't huge (one less cap and resistor, one more pot), but the layout may be easier.
Yeah, I will definitely consider that.
Was surprised you said it looks "neat". Somehow, the pics make things look a bit better than they really are.
I just have a feeling this is going to be a trouble-shooting nightmare where noise is concerned. Stuff on both sides of the Board/Chassis.....wires going under and over everything, etc. etc.
Anyway.....Thanks Again.
I will be back
