Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tom_Hull on November 03, 2013, 05:51:15 pm
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hi
It looks like the pt I want use for the 7591 tubes needs a doubler .
I was wondering ??
If the PT has 175 volts on the hv wires ,red and red yellow.what may be the voltage using this doubler.??
the amp is in an organ with a load the voltage is 420volts.
thanks
tom
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175vac on the PT?
Then 175 * 1.414 = 247.45v -> 247.45 * 2 = ~495vdc.
Minus diode drop, and minus whatever sag happens as a result of the output tubes sucking current from the stacked filter caps. But the total stack of filter caps needs a total voltage rating of 500vdc or better.
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hi HotbluePlates
thanks lots
500volt caps or better ,and sluckeys suggestion of 220k resistor for the first stack of caps .
ok still checking this organ circuit ..
tom
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The diode configuration you show is *not* a voltage doubler, it is a (full-wave) bridge. It's just not drawn like most bridges are....you know, diamond-shaped. You have: 4 diodes; your AC is fed to the two diode junctions where the diodes are "different", eg; of opposite directionality...and the B+ is taken from the junction of the two cathodes ("bar ends") while the B- comes from the junction of the two anodes.
The most common form of voltage doubler has but two diodes and is characterized by series-stacked filter capacitors. It's half-wave. It's also possible to use 4 diodes in a full-wave voltage doubler but ALL voltage doublers will have stacked (series connected) filter caps. A full wave doubler will almost certainly sag less and produce a slightly higher stable output voltage.
HBP is correct that the output of the ckt as drawn should be about 1.4 times the input voltage. A doubler whether half or full wave should produce more volts, much more like "double" the AC feed, will but be a little more sag-prone.
Pay attention to that .22 cap coming off one side of the HV AC secondary for the bias. In the circuit as drawn it is technically not needed but it is DEFINITELY needed should you decide to morph the ckt into a voltage doubler.
Yes, it is true that in your dwg you have two series-connected caps...but nothing is connected to their midpoint. The essence of a voltage doubler is those series connected caps, and one conductive phase of one diode charges one cap and then the other conductive phase thru the other diode charges the other cap in the stack.
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The diode configuration you show is *not* a voltage doubler, it is a (full-wave) bridge. ..
True-dat.
I didn't pay attention to the schematic fragment, as the tubes seem to be taken from one thing, the PT from another, and the schematic fragment seems like it would be something else... otherwise, why ask what the output voltage will be when it's already indicated on the schematic?
... the output of the ckt as drawn should be about 1.4 times the input voltage. ...
Yes. The bridge originally shown, or a bridge on any non-center-tapped winding will output 1.414 times the end-to-end voltage of the winding, minus diode drops and sag. With 175vac, that leaves you at 247.45vdc, minus drops.
Obviously, a doubler circuit doubles that to 495vdc. But ripple voltage will be higher and the ripple frequency will be 60Hz instead of 120Hz. The output voltage will sag quicker because the caps receive a full charge 60 times per second instead of 120 times per second.
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Gotcha, HB!
"why ask what the output voltage will be when it's already indicated on the schematic?"
I think he is copying the general power supply ckt (..tubes seem to be taken from one thing, the PT from another) which yes, shows the output voltage but does not show the tranny (AC input) volts...the lack of that relationship is what the mystery is about.
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hi sorry for the confusion .
just put 30 hours of study into these amps
the answer I needed was the voltage obtain from the use of a voltage doubler .
a big voltage number .
also the power string,,,,,, instead of taking it off the yellow red lead at 210v as the organ does.
and the power circuit in the organ has resistors in it .
now what is going on in this organ . its going to stop working soon . and its to much to fix,70 tubes ,,,,
its so old with bumblebee caps .I have enough bumblebees and organs already .
I think they used zenier diodes ,there are 2 funny looking metal diodes on the HV red line to the ground. a resistor before getting to the cap. ,,,,,,,,,and one more on another lead for a different circuit .. i never seen some before.
i 'll draw a circuit
thanks
tom
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Diodes come in a variety of shapes. A common design for small rectifiers or zeners is the top hat. It actually looks like a small top hat. What are the numbers printed on the case?
Drawing the circuit, or otherwise providing a schematic and even telling us which organ would be very useful. Actual pics help to.
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Build the voltage doubler by tacking the components together and let them hang in the air. Lash it up to the HEATER winding. Power it up. Measure AC input (to the rectifier, I mean) and measure DC output. That's your input:output ratio. Of course, you need to simulate the load on the supply. Any half-wave rectifier ckt will sag more than a full wave rectifier, and doublers are no exception. Now if you do this (rectify the filament winding versus the HV winding for your test) from an ORGAN transformer that might have 8-10 amp capacity (because it ran 50 tubes) then the effect of your load will be less, proportionally, than it would be on the HV winding. Take that into consideration.
It is not that easy to figure the output of a doubler with precision, that is my experience. One reason is because the series caps on the output act like...you guessed it, series caps. You can build up the output voltage by going with a full wave doubler. You can lower the output voltage (slightly) with balancing resistors across the two caps (I recommend this) and an overall bleeder resistor. Of course you don't want to have throw a 100 watt bleeder in there.
Doublers work. They need not be feared. I will repeat you MUST have that fat .22 (or so) series cap going off to the bias supply if you are going to steal one side of the HV winding for your bias.
I am building an amp now that requires a doubler, basically because I've committed to using the power transformer which is a weird thing with a 126 volt winding and 2 qty 22 volt windings. (yes, I am demented) I'll be using 2 or 3 of those windings in series as required. I am building the rectifier section using sufficient extra terminals strips such that if I need to make it full wave vs half wave (two more diodes) I'll have them.
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hi
there are numbers are small on the diodes 7109 FA273A .
here is a pic
diodes
organ Lowrey dsl
and the ladies 12ax7s
on the organ there is a cap and resistor connected to the red yellow wire . going up into the keyboard area.
I have drawn the circuit without the extra cap and wire
(http://i42.tinypic.com/9hrujp.jpg)
(http://i41.tinypic.com/r8fndh.jpg)
(http://i39.tinypic.com/24bkphc.jpg)
(http://i42.tinypic.com/9hrujp.jpg)
(http://i39.tinypic.com/jtkpsi.jpg)
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Man, you are lucky getting all those 12AX7s. Who is the maker of that organ? Those tubes were all 12AU7s in the CONN I got a while ago, a vastly less useful tube.
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Man, you are lucky getting all those 12AX7s. Who is the maker of that organ? Those tubes were all 12AU7s in the CONN I got a while ago, a vastly less useful tube.
hi
some of my pics I posted are with reverb... :l2:
yes the keyboard note area are not 12ax7s,,, more what to do with these ,, tubes
just the preamp has the ladies waiting to sing >
I have way to many 12 ax7 s. and 12au7 s
as I have no amp for them .
so maybe in stead of a twin for an amp I will put two more transformers in and make a QUAD. :think1: WITH A LESLIE
then use some 12ax7s and some more 12__7 types ..ya more tubes
tha
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WITH A LESLIE
Yes save that Leslie. You can make or have a cab made for it.
Brad :icon_biggrin:
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By the way, those "top hat" diodes are what many of them looked like in the late 50's. Nowadays, the same performance/ratings are typically achieved in a little black mouse-pellet 1/8" in diameter and 1/4" long. The heat sink for diodes is their leads. Back then, the leads were made bigger and longer off the body of the diode because it was either thought or required that the extra metal was needed. A 1N4007 1000v/1 amp diode probably outperforms the vast majority of rectifier diodes from the era.
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WITH A LESLIE
Yes save that Leslie. You can make or have a cab made for it.
Brad :icon_biggrin:
Hi Brad
yes .going for it
because of the wattage .there is another stationary speaker in front of the organ working with the leslie.there are 4 speakers ..
The speaker in the leslie is a jenson special design.. I lucked out there .
hi eleventeen
thanks for that info .. I have a few of those ..
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hi
this is close to, what I thinking of making.
I found a good schematic. of Ampeg ET-2B super echo twin amp, with the voltages . from the back panel of one .
but the voltages a way different from my PTs voltage output .
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... what I thinking of making. ... but the voltages a way different from my PTs voltage output .
The easiest path to a properly-functioning amp is to use the power transformer you have in the exact same circuit it was used in before you removed it. In fact, copy the whole power supply and output stage up to about the phase inverter, and then tack on a different preamp to your liking.
My advice might be different if you weren't starting with a specific PT.
Example:
You just copped a great old Stancor PT, but it's 450-0-450v. You also have a couple of EL34's, and have visions of a 50w Marshall. Didn't some of them have high B+ near 500vdc? But your PT has a center-tap, so a bridge outputting 450*2*1.414 = 1273vdc won't work, and even a full-wave rectifier outputting 450 * 1.414 = 636vdc is too much. You look up the amp this PT came from and see it has a full-wave rectifier feeding a choke-input power supply. That gives 450v * 0.9 = 405vdc which is perfect as long as you have that input choke and maybe a second one for an additional stage of filtering for screens/preamp. EL34's could idle at 25w/405v = 61mA each, which would pull enough current through the input choke to maintain good filtering for a beefy ~25w class A.
The PT in that example just doesn't want to be used any other way with any other common setup. You'll find if the donor amp doesn't use a setup exactly like every other guitar amp, it may not play not when you try to make it like every other guitar amp.
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Hi HotBluePlates
thanks lots
ok then .
well this is what I am up to with the original
so working on one of the phase inverter schematics.
12ax7 and two 7591
there is a quick one ....nothing is checked over and just reading the resistors without aid .. I need to do the values correctly..
the resistors have drifted and maybe a dead resistor..in there
.the wire colours maybe are ,, not the right color as they look blackish in color
tom
(http://i40.tinypic.com/k34orr.jpg)
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I'm thinking that bottom .047µF really connects to pin 1 rather than pin 2.
170K resistor? That's brown/violet/yellow. That's a value I've never seen.
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I'm thinking that bottom .047µF really connects to pin 1 rather than pin 2.
170K resistor? That's brown/violet/yellow. That's a value I've never seen.
Hi Steve.
yes you are correct on both counts .
the resistor is a 150K not 170k
ill get this done correctly .soon .
thanks
tom
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Here's the easy way to get to 1MV. No diodes and only 1 cap.
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hi
lipstick can feel deadly,,.be kind.
I check out the schematic
of this 3 million volts
http://nservices.com/stun.htm (http://nservices.com/stun.htm)
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Hi
well now I have something confusing me ..
about the power cord going into the amp
I tried posting a pic but the camera batteries are dead again .
I'll describe what I see.
so the power cord
black wire ac connects to a fuse and connects to the transformer
the red wire connects to a 100k resistor and then connects to ground .
I guess it reduces voltage \///???
tom
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Hi
well plans dropped for now ..
So I turn on the organ and its sounds so good ,even with is problems .
well decided to.. fix it enough and later restore it instead.,,,,,,, 70 tubes sound great
I want to build something for me for an acoustic guitar .. :l2: :l2:
or finish building the vox .ac 15 30. but I really enjoy my M12 ampeg with my old tubes ..
Even if I cannot play guitar ,,my kids can play them..
thanks ALL
tom