Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Planobilly on November 15, 2016, 06:25:51 am
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Hi,
Do you guys have any advice on power transformers to use for general experimentation?
This transformer will not be the final transformer used in any particular amp but a transformer that could be temporarily employed in a prototype. Something that could power up to a 100 watt amp. Something that perhaps has multiple HT taps and heater taps. It would also be useful to be able to create DC heater voltages.
Thanks,
Billy
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Some time ago someone posted a link to such a transformer, unfortunately I don't remember more
An alternative can be to get a big enough PT that has a redundant HT and use a VVR to drop the voltage to the level required by the circuit on the bench
One other alternative is to use a pair of 220V insulation transformers and connect the primary in parallel and the secondary in series (440V AC)
use a VVR as told and 6V and 12V transformers for filaments
To manage the HT instead of a VVR, if you have one, you can also feed the insulation transformer using a Variac on the primary
Franco
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This isn't an all-in-one, no filament taps, but for a breadboard it's the one I choose. manly for quick n easy B+ changes.
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Ehy Shooter, you've just hit the target at center
that is the transformer I remembered
Franco
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If you are going to buy such a transformer NEW, it's probably going to be a $65 -$80 thing with a delivered cost of nearly $100.
As an alternative, might not you be better buying a used Heathkit PS-4 power supply? There's one for sale near me for $69 which is pretty cheap, but for $100 you could probably get a complete regulated power supply, with 4+ amps heater, usually a bias supply, and METERS which are very handy.
My photobucket is goofy right now, else I would post a pix. Google images "heathkit PS4" (or PS3) or IP-32 or several other Heathkit models.
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a Hammond 272JX will do what you describe. Plenty of current for 100W and both 6.3V and 5V taps.
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a Hammond 272JX will do what you describe. Plenty of current for 100W and both 6.3V and 5V taps.
MakerDP, how do you vary the HV on the 272JX? It seems it is limited to 300V or 600V.
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I bought a SW radio (shortwave), several years ago, it came with a separate transformer. The transformer had multiple taps for power as well as multiple taps for heater filaments. I would therefore, check out SW radio websites, and any swapmeets.
Those sw guys do crazier stuff, than the guys on this formum. :icon_biggrin:
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Those sw guys do crazier stuff
it's all that high frequency RF so close to the brain cells :laugh:
Edit; Untangled quote, Willabe.
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I purchased a power transformer a few years ago from Weber that had this feature. I still have not used it, it is one of those "will use it eventually type things"
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Do you guys have any advice on power transformers to use for general experimentation. . . Something that could power up to a 100 watt amp.
This is a recurrent topic. I submit that there is no such transformer. The Weber PT suggested by TubeGeek is probably the best all round choice, though it's not clear it could handle a 100W amp. One issue is sag, and do you want it. A PT with enough heft to power 100W without sagging will simply not sag if and when you want it to. Another issue is the secondary voltage supply, which invokes bias and Class of power tube operation.
Another option is a standalone bench top power supply. But these are regulated and do not behave like a guitar amp PS.
IMHO a big tranny or a variable bench top PS are useful for diagnostics and testing, or for hi-fi amp design. But exact PT selection -- as to both voltage & current -- is critical for guitar amp performance & tone. (True also for OT.)
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As I have read the post here it looks like there is no easy solution to the issue. I am only building and repairing guitar amps. I am only using readily available JJ current production tubes.
I have about come to the conclusion that the only workable solution is to buy around a thousand or so dollars worth of OT and PT in the normal range of stuff I have an interest in. Actually I have a few now. They are mostly Hammond and Magnetic Components OT and PT.
I use Mercury Magnetics and Chris Merrien when I can afford too. Hammond and Magnetic Components when cost is an issue. I use a few other brands when I get stuck with things being out of stock.
Mercury Magnetics are good transformers but they are damn expensive if you have ordered less than 25 from them. At that point they will discount by 40% which brings them in line with other good brands.
I am just a old retired guy and I don't have or want a "real" business. I do all this because I like it, so profit is not my primary motivation.
Thanks,
Billy
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This is my idea for a cheap Bench AC PS
The PS use a Variac (you can use it in many circumstances)
a pair of 120v/220v transformers (or 220v/220v if in your country you have 220v lines)
and a 120v/6v+6v transformer (may be those used for lighting)
(http://i.imgur.com/oquSsnz.jpg)
This way you have 6v or 12v for heaters and 0-220v or 0-440v AC for B+ (0-308v DC or 0-616v DC rectified and leleled)
Franco
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a Hammond 272JX will do what you describe. Plenty of current for 100W and both 6.3V and 5V taps.
MakerDP, how do you vary the HV on the 272JX? It seems it is limited to 300V or 600V.
To lower the voltage there are plenty of well-documented tricks including zener diodes, VVR or fixed-MOSFET dropping.
It is limited on it's upper range but it's max voltage will be plenty for most every guitar amp application.
The problem with using a variac is that it also reduces your filament tap voltages. So, unless you are running a separate 6.3V/5V supply transformer(s), a variac may not be the right way to go about this.