Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: silat on July 07, 2024, 04:10:37 pm
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What to build? There is no bias tap. Can you make an artificial bias tap using only diodes and no tube rectifier?
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These are not pictures I had taken, but they are the same exact transformers I have. So used them/lifted from the interwebs.
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I'd suggest a cathode biased 6v6 or el84 p-p amp with similar voltages. I'm not sure how much current draw your PT is designed for, but I'd bet it can handle at least three preamp tubes. The silvertone 1482, fender 5E3, tremolux, vox ac10, could be close but not perfect fits. I'd recommend finding something that you want to make and understanding if the differences in your transformers is too great to make them happen or no problem. Enjoy the journey!
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You can obtain a Bias supply from that PT this way
Franco
p.s.;: if you have a Google search for Bias supply from HV winding you'll find schematics and explanations
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Do you know what it's out of?
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You can obtain a Bias supply from that PT this way
Franco
p.s.;: if you have a Google search for Bias supply from HV winding you'll find schematics and explanations
Franco, Thank you. That is what I wanted to know.
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Do you know what it's out of?
Yes, It is out of an old Hammond organ organ: M-111 I think it is not the Field coil type.
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You can obtain a Bias supply from that PT this way
Franco
p.s.;: if you have a Google search for Bias supply from HV winding you'll find schematics and explanations
I have part of my rectifier done by diodes, but I did not fully understand How I was supposed to go forward with it. I will have pictures in a few hours or as soon as I can.
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Here are the pics. I put the transformers in a Magnavox chassis. I was trying for something Marshall with 6v6 but was confused about the bias tap sense I did not have one. I looked up artificial and it confused me even more.
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I had the Long narrow Hammond organ amp chassis, but it is to narrow and to long, no room for anything.
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I had the Long narrow Hammond organ amp chassis, but it is to narrow and to long, no room for anything.
I guess I could go PP 6v6 with something more simple like a 5E3, but I am not very fond of them. I have a megaton of 6V6 Tubes and some 12AX7's. I want to use what I have.
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Just a thought to consider. I am not saying you should pursue this. I probably have a layout available if you're interested? However, you may prefer point to point given the chassis layout you have?
This attached layout should work OK. IF there is a discrepancy between the schematic and layout, use the schematic as your guide.
With respect, Tubenit
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What is your PT's part number?
I've used transformers from an A0-43 chassis to make a Princeton 6G2, an AB763 Deluxe Reverb clone with JJ 6V6s, and an 18 watt with 6BQ4s (EL84s). If you try different rectifiers and dropping resistors, you can get a range of B+ voltages. With a GZ34 it can put out more than 400 volts, with a 5Y3 it's more like 325 volts at the plates.
Here's a schematic to show the bias supply I used for the DR. It can range between -25 to -45 volts, but you can season to taste. Sluckey explains explains how to tweak a bias supply to get the range you want: http://sluckeyamps.com/misc/Amp_Scrapbook.pdf (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf). He explains the theory so simply even I could understand it. :laugh:
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Just a thought to consider. I am not saying you should pursue this. I probably have a layout available if you're interested? However, you may prefer point to point given the chassis layout you have?
With respect, Tubenit
What Is a Hoso56? I am not familiar with it. Can you give the Layout also? My heart is not set on any one thing.
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What is your PT's part number?
PT A0-24110-1......... OT A024924
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HoSo56 amp (el34world.com) (https://el34world.com/Forum/index.php?topic=6176.0)
With respect, Tubenit
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The Amp sounds like it would be something I would really like. The one problem I have is I would have to buy most of the tubes. I don't think I need the reverb version. I just built a 6G15 clone out of an old reel to reel I had and it is surf city. Plus I have a reverb pedal that is fantastic. I think it it would be worth trying to build, the way you all talk about it.
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The one problem I have is I would have to buy most of the tubes
I have a megaton of 6V6 Tubes and some 12AX7's.
What am I missing - if you make the SoHo 6V6 you need 1 5879.
If you make a Plexi 6V6 - you need to buy no tubes.
You could also make Doug's 18 Stout as a 6V6 version.
Regardless, I think its hard to go wrong with any of Tubenit's, Sluckey's, or Doug's projects as you will get super help along the way. And Hammond organ iron is great - I've built numerous projects with them.
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The one problem I have is I would have to buy most of the tubes
I have a megaton of 6V6 Tubes and some 12AX7's.
What am I missing - if you make the SoHo 6V6 you need 1 5879.
If you make a Plexi 6V6 - you need to buy no tubes.
You could also make Doug's 18 Stout as a 6V6 version.
Regardless, I think its hard to go wrong with any of Tubenit's, Sluckey's, or Doug's projects as you will get super help along the way. And Hammond organ iron is great - I've built numerous projects with them.
Yeah you are right I looked at the wrong schem. I looked at the one with 6Bm8 tubes.
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And Hammond organ iron is great - I've built numerous projects with them.
+1
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Just a thought to consider. I am not saying you should pursue this. I probably have a layout available if you're interested? However, you may prefer point to point given the chassis layout you have?
With respect, Tubenit
Tubenit PM sent
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You can obtain a Bias supply from that PT this way
Franco
p.s.;: if you have a Google search for Bias supply from HV winding you'll find schematics and explanations
capacitor coupled bias supply is another method - for High Tension supplies using FWB rectification (at bottom of page in this link)
http://www.valvewizard.co.uk/bias.html (http://www.valvewizard.co.uk/bias.html)
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This is basically Hoffman's bias supply that I re-drew for my version of his 6V6 Plexi because making my own drawings helps me understand the circuits better. And, it's half the fun of the project for me.
You can see that the 220K/3W resistor connects right off of one of the red PT secondary wires before they connect to the rectifier diodes. My PT has no bias tap.
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I had the Long narrow Hammond organ amp chassis, but it is to narrow and to long, no room for anything.
There’s the long narrow Hammond AO-43 chassis with a 6V6 Plexi, a little tight but a nice small head and great Marshall tone. You’ll have to cut the EL84 holes out and put a plate over for 6V6’s sockets.
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Is that PT from an AO-43? It looks like the one from an AO-63. All my 43 chassis have smaller PTs.
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Is that PT from an AO-43? It looks like the one from an AO-63. All my 43 chassis have smaller PTs.
It says A029 on the Chassis.
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I have an Ao-29 here, and I haven't done anything with it yet.
I think the PT/OT pairing would be a good suit for a deluxe/princeton reverb type build.
I only say this because there's a pile of little tubes drawing on the heater string, and the B+ in general.
I think if I were to build a plexi or bassman type circuit I'd use 6L6's with an OT upgrade.