Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chuggy on November 07, 2010, 12:31:10 pm
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I'd like to substitute diode rectification in my Kay 703 which has a dead 35Z5 half wave recto.
Would this involve a single diode or string from cathode to plate? What diode(s)? A resistor to substitute for the series heater would be needed. The data sheet says heaters run at 35 V with .15 A current.... so 233 or so ohms bridging the heater connections?
THANKS-
JIM
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You can use a single 1N4007. Put a sag resistor in series with it to keep the B+ about where it was with the tube. I'd start with 100Ω but experiment to find the best value.
Your math looks good for the filament replacement resistor. Use at least a 10 watter.
You can buy a 35Z5 for $9 at AES (http://www.tubesandmore.com/). They also have a 35Z4 which should work fine for $2.50.
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Unless the filament is out, just wire a 1N4007 across pins 5 and 7 and leave the tube in. B+ will go up so use 200V or 250V filter caps.
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... B+ will go up so use 200V or 250V filter caps.
Which means buying a new can cap in that amp (in all likelihood). That can costs several times more than a new 35Z5. So it seems like it's "cheaper to keep her."
But maybe you needed new filters anyway. Will a new can rated for higher voltage (due to less diode drop) fit in the old space? Usually there's no room to spare on this type of amp.
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Can was replaced with individual caps that fit easily.
Got a NOS 35Z5 via ebay for $1.04, so diodes on hold.
Jim