Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Esquirefreak on August 29, 2022, 02:30:20 pm
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So... I've run into trouble with a new reverb unit build. At the DC end of the rectifier diodes I'm only getting 170VDC.
I've built the reverb using Tubeswell's hum loop blocker schematic, but I'm using a Hammond 261D6 PT (250VAC CT).
I just now noticed that his schematic says 240-0-240, which would make that 440VAC CT, right?
I've got 7.04VAC unloaded filament and there's 270VAC between the secondary HT leads.
× Am I missing something or am I simply using the wrong PT?
× Should I lift the HT CT and ground one of the HT leads (where the CT currently is connected) and then use the original 3-diode string?
Best regards from Sweden.
/Max
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I'm only getting 170VDC.
I'm using a Hammond 261D6 PT (250VAC CT).
250V CT is same as 125-0-125 and 170VDC is all you can get with your rectifier circuit. You can get 350VDC if you rewire those four diodes as a full wave bridge rectifier.
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The previous one I built has a 290WEX PT (237VAC-0) and all voltages were right on spec. One of the HT leads grounded. That's why I thought maybe I could get 250VAC-0 out of this PT by lifting the CT and grounding the end of the coil.
If I were to rewire the diodes for FW rectification, how do I ground the CT? It would bring a lot more clarity to me if I could see it drawn in a schematic...
Sorry for being stupid :laugh:
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if you use a full wave bridge rectifier you would lift the ht center tap (cut the wire and heatshrink it)
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http://sluckeyamps.com/revibe/revibe.pdf
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I'm so glad I have this forum! Thanks a bunch. Will be re-doing the rectifier tomorrow.
Here's the cab I finished today. I tried to make it look like a '61 rather than '63.
I'll update when I've got it up and running!
/Max
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It's very easy to convert your rectifier to a full wave bridge. Just move the PT wires around and ground the negative side of the bridge. Don't use the PT center tap. If you get stuck, post a hi-rez pic of your diodes and we can help.
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I just now noticed that his schematic says 240-0-240, which would make that 440VAC CT, right?
Yep for a 2-phase rectifier, you use one side of a centre-tapped HT secondary to calculate the B+, i.e.; 240 x 1.414 = 339VDC.
(But that's different to how you rectify a High Tension winding where you don't have a CT, and the others have already picked up on that)
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Up and running!
306VDC at the plate of the 6K6 and dissipating 7.9w at idle. It's early morning here now and I just got back from my graveyard shift. So I'll sound check later today :icon_biggrin:
/Max
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Nice workmanship! :thumbsup:
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I finished one too 2 weeks ago... but I had to put in a 6V6GT. With the 6K6GT it was showing blocking distortion...
I built the cabinet to accomodate with my 18W Tremolo TMB 😉
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That's a pretty build, right there!
I moved to a new apartment last month and since I have a spare room, I finally have a space dedicated to amps and guitars. Also, now my cats won't be able to chew up every single cable I have on the floor...