Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on March 25, 2014, 01:05:42 pm
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I think that it can be done, but not sure 100%
The PT has a 3.15v-0-3.15v winding plus a 0-5v-6.3v winding, so if I want, I can connect the relays to the 3.15v-0-3.15v winding
but I would like to know if to connect the relays to the 0-5v part of the 0-5v-6.3v winding used for the rectifier heaters is doable and safe
Thanks
K
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I need to see that winding grounded some where. The EZ81 heater is insulated from cathode by thin ceramic mud. If it breaks-down, there's +400V from the cathode on your relay wires. I think you can just ground the end of the winding that connects to DC cap and heater. Now if the heater insulation breaks down, the EZ81 or the PT blows-up before you can be shocked and die.
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Thanks PRR
Reading your explanation I think it will be better to avoid that solution and use one other winding for relays
K
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Why don't you connect the relay on heater winding with resistor to drop to 5 volts ?
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The PT has a 3.15v-0-3.15v winding plus a 0-5v-6.3v winding, so if I want, I can connect the relays to the 3.15v-0-3.15v winding
but I would like to know if ...............
Was only technical curiosity
K
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Another option would be to put the EZ81 on the filament winding with all the other tubes thus freeing up the 0-5-6 winding for your relay supply.
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Wouldn't that draw too much current though? I peeked, and the EZ81 needs 1 amp all by itself.
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Too much current for what? The PT filament winding has no current rating specified.
Many amps have the EZ81 on the same filament winding as all the other tubes. Hammond AO-44 and Vox AC-15 quickly come to my mind.
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I agree with Steve,
some time back I asked and someone confirmed me that rectifiers like ez81 can be connected on the winding for heaters of other tubes of the amp
In this particular case the transformer is this
http://www.inmadout.com/download/pdf/TA84M18.pdf (http://www.inmadout.com/download/pdf/TA84M18.pdf)
and the amp is a 18W jtm45 (with Mr. Merlin Master Volume mod as input)
3 x 12a*7 tubes = 900mA
2 x el84 tubes = 1520mA
total current required for tubes = 2420mA
K
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Okay, cool. I did not know that! (in my best Johnny Carson voice)
*edit 1* Just thought of something though, why would they spend money on a PT with the extra winding if that was the case?
*edit2* Re-read, re-thought. In amps designed that way, maybe there is no 5v extra winding. (you guys always amaze me with the schematics you have in your head, while I have none) Looking at the PT spec sheet, the 6.3 winding is spec'd at 3.2 amps, so if he adds the EZ81 it'll be drawing 3.4 amps. Maybe it gets a little warm, maybe not?
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why would they spend money on a PT with the extra winding if that was the case?
Who is "they"?
We're talking about a separate filament winding for an EZ81, right? The EZ81 is only gonna be found in the small amps. None of the big names, ie, Marshall, Vox, Hammond, etc. had a separate filament winding for an EZ81. After all, it was designed to work on the same filament string with the other 6V tubes, and adding another winding just messes with the bottom line. Even the very popular Marshall 1974 18 Watter started out with a single filament winding.
I think it's a great idea to have the rectifier on a dedicated winding. And today so do a lot of Booteek builders, and transformer manufacturers.