Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jerome on February 25, 2016, 09:18:45 am
-
I recently gutted my Hammond AO 43 leaving only the power transformer, tube sockets, choke, and output transformer. I bought a Blues Jr conversion kit and I wanted to know if I could use the rectifier tube in the AO 43 and also was not sure were the wires to the choke go. I have a red and blue wire. I have power to it and it plays but is cooking my power tubes I hooked the choke up to blue wire to pin 8 on the rectifier tube and to B+ on my board were I also have the red output transformer wire. Im super new to this but really want to learn. Thank you! :dontknow:
-
Damn! I thought I could actually offer some answers instead of asking endless questions but, alas, it sounds like i'm only about a week ahead of you in this whole deal.I do know that when I've used chokes they were always in place of one of the resistors in the power filtering rail. But for God's sake don't take anything I say as advice. But welcome to the club. I'm super new to this as well but I'm completely strung out on every aspect of it. The folks on this board have been incredibly helpful and patient with me. Someone'll sort you out.
-
Please post a schematic of your AO-43. I found something online under the L-100 organ, but not sure it matches your amp. In the schematics I found I see no choke (though there is an SE tranny that might look like a choke powering the reverb driver tube).
Also, chokes have no polarity. And, typically in these amps the choke feeds the screen supply, and comes after the plate supply.
What BJr kit do you have? Have you built it yet? Not clear from your post.
-
I bought a Blues Jr conversion kit and I wanted to know if I could use the rectifier tube in the AO 43
If you are using the original AO-43 PT then you can use the rectifier tube. ***CAUTION*** YOU CANNOT USE A BRIDGE RECTIFIER WITH THE AO-43 PT! If you try, your B+ voltage will be twice as high as you need and will likely kill your tubes and some other stuff.
You can use the choke. Just remove the 2.2K/3W resistor located between points "B+" and "Z" and connect the choke wires where the resistor had been.
***CAUTION*** This conversion kit was designed specifically for a Blues Jr. It cannot be used in a different amp unless you know what to do. For example, there is no bias winding on the AO-43 PT. That means you'll need to adapt that conversion board to use the high voltage secondary to supply AC to the bias diode. This is the most likely reason your output tubes are burning up. So, don't put any output tubes in the amp until you have approx. -15VDC on pin 2 of both output tube sockets. It's an easy task to do but if you get it right the amp will continue to just burn up your output tubes.
PS... I changed the topic to something more meaningful. You can change it to whatever you like.
-
In the schematics I found I see no choke (though there is an SE tranny that might look like a choke powering the reverb driver tube).
That's not a SE tranny. That's the choke. It's CH301, a 14HY choke and it's used as the plate load. The plate is actually cap coupled to the reverb tank. That choke works well in my Plexi6V6 power supply and will work well in this BJ too.
-
Thank you so much Sluckey! Great advice and I have taken all of it. I did find out the choke was for the reverb and I dismantled the reverb all together. I took everything out and stripped it down to the tube sockets . I think im going to go ahead and buy a blues jr power and out put transformer and skip the rectifier tube. I went back to my Fender blues Jr and put the conversion kit in it. I have low volume no clean overhead and only gain. The meat pot in place of the reverb does absolutely nothing. There were a few resistors I had a hard time identifying, they were the 820, and the 82k. I also had a hard time knowing what end to read on the resistors. For example the 10k and 120K I may have them switched around. At least on old resistors the colors are clear. Thank you again I really appreciate this!
-
The 5 band resistors can be confusing to determine the values, especially if the body is blue. If you are unsure of the value, use your ohm meter to confirm the value.
-
When biasing a Blues jr after conversion do I check the voltage drop at the + main filter cap and the +of the bias diode? With or without the el 84s in?
My Master volume at 1 starts to break up, I have lots of power no clean. I can see one of my El 84s glow blue when I strum a chord. Should my bias be set at 3.4 voltage drop higher or lower? :help: :help: :help:
-
Do you have a Hoffman BJ conversion board? If so, measure the voltage across the 1Ω cathode resistors. Look at the schematic.
-
Yes I have a Hoffman Jr kit. Thank you once again :worthy1: Im am so new to this but really enjoy it and want to learn more. Your help is greatly appreciated. I also stay away form the internet but this forum and site is my favorite place on earth now! I am now going to attempt to take my Hammond organ chases put a Hoffman Princeton reverb guts in it and put it into a suitcase with a Whirlitzer alnico speaker in it. Im sure I will have a million questions for you Sluckey. Thanks again brother! Oh yeah the Blues Jr is rocking! I miss the reverb a bit but this thing is so solid and has new grit. I will recommend the Hoffman conversion to anyone with a Blues Jr. I had a blast learning about it.
-
I just finished my Princeton kit and 6v6s are cooking. Where do I check the Bias and what should it be set at?
-
It works! I cant believe it really works! I dont like poking test meters around in a live amp so can someone please let me know where I check the bias on a Hoffman Princeton reverb and what range should I look for in a 6v6? This is my first 6v6 amp I have always had El84s.
-
I answered in your other thread.