Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => AmpTools/Tech Tips => Topic started by: overtone on October 13, 2011, 12:41:41 am
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There ia a homemade OT tester up on the German fleabay site this week (item 170710642418)
A paraphrased translation with the part of the description that caught my eye underlined:
- homemade tester built for testing pp OTs while in the amp and disconnected from the main power supply.
- Designed for 6L6 & 5U4 as a rectifier.
- the octal plugs plug into the sockets of the amplifier.
- 2 red bulbs indicated the failure of an anode voltage winding.
- must be powered by external 6.3 volts and 250 to 350V AC voltage. Transformer not supplied.
- Rectifier and filter capacitors in the device.
- Tube complement 2 x 6L6 and 1 x ECC81 (phase reversal)
- 1 audio input with volume control in the device.
- Schematic is included
- device is in working condition.
- "You can build a monoblock out if it."
I'm not interested in bidding because it seems to me a very involved way of testing the anode windings of an OT, or am I missing something here?
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Looks like a small mono amp with a couple of meters and some leads which plug into the DUT using it's PT tubes sockets.
Not worth the bother IMO.
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A guess regarding the red bulbs:
A properly functioning OT should be a somewhat low resistance from the output tube plate pin to the OT center-tap. Due to the use of the plugs for both the output tubes and the rectifier, you have access to these two points at the tester.
If the bulbs were somewhat high voltage neon, then they would be off when the OT winding has continuity, and light up only when there is a significant voltage difference between the winding end and center-tap, such as when the winding is open. I guess the bulbs could be incandescent, but they would have to be high-voltage types to keep the filament from popping with an open winding.
And you use one bulb per OT half-primary.
This tester is a mystery to me. It looks quite well built, with quality parts and construction. Someone had to spend some money (and time) to make this. That only makes sense if you have to test a LOT of amps for OT faults. But if you're mainly finding out if there's an open, why can't you just stick your meter probes into the output tube plate and rectifier cathode socket pins? So that makes me wonder about a production situation, where you might not have time to pull the amp out of the chassis. If so, why not test the OT before the chassis goes into the cab, or before the OT is installed on the chassis?
It seems like maybe someone got carried away building the ultimate tester that they don't need.
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Hi Overtone
- Schematic is included
can you post the schematic ?
I tend to don't understand if I do not see a schematic (and many times not even that is enough !)
Thanks
Kagliostro
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It seems like maybe someone got carried away building the ultimate tester that they don't need.
I think you hit it right slap bang on the nail there!
The red lights interested me, I was half imagining some kind of built in current limiter.
Hi Kagliostro,
I agree, I also like to see a schematic, or draw one if there is not one.
But this unit is not mine and I did not build it.
It was for sale last week from someone on Ebay.
It was difficult for me to understand why anyone would build this tool.
Best, tony
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Oh OK Toni
I misunderstand you, I was thinking you get it
Kagliostro