Josey,
I have all the parts on hand to build you a board, so no worry about funds yet - I think shipping will be more than parts. I am going to Florida for Thanksgiving, so it will be after that that I finish it.
Here is the formula I used (Bruce deserves a lot of credit for making the instructions clear enough that I could figure it out without having to ask a bunch of questions) -same parts too: http://audiokarma.org/forums/index.php?threads/show-me-your-ibam-ibba-2016.713900/
And this is where I mounted it - just made one of the transformer studs long and mounted it between two nuts.
View attachment 1329756
I can build you one of these, but it will cost you, and it's not very easy to deal with replacing the can cap.
View attachment 1329758
Wow! That is awesome! And highly convenient! I'm going to need to look into that. Thanks!Josey,
Its really handy to have your power tube bias adjustments above board vs inside the chassis.
Here is what I did on my 500B:
View attachment 1329856 View attachment 1329857 View attachment 1329858
Also if you look close you can see where I cut the can cap's when I re-stuffed them.
I think i see it right a the beveled edge? How did you cut it so perfectly?Josey,
Its really handy to have your power tube bias adjustments above board vs inside the chassis.
Here is what I did on my 500B:
View attachment 1329856 View attachment 1329857 View attachment 1329858
Also if you look close you can see where I cut the can cap's when I re-stuffed them.
I think i see it right a the beveled edge? How did you cut it so perfectly?
I had no idea!! LOL.Josey........
I bet you are seeing how this restoration/modification thing can grow. LOL
Thank you, I will check that out. The amp came with an 800-C manual and schematic in the box. I'm wondering how different that is.Josey,
Here is a schematic for a 500C with IBAM and some other mods. The 500B is similar enough so I built my IBAM as shown in the schematic
Edit: I can't figure out how to put the schematic here.
It's in the AK Database.
I'm definitely considering the can cap bias too! Oh, the choices! LOL!I bought the pot's and test jacks on ebay. Then cut and bent the aluminum sheet metal just big enough to mount them.
Search for some 10K trim pots designed for panel mount.
The remaining components are on a board directly under and inside the chassis, the 500B has some open space there.
I had the metal plate bent at work
You could do pretty good with a bench vice.
Matt's can cap bias assembly is a sweet setup though!!
The 7591As in question were purchased new in about 1985, installed in my 500-C which was used for a short time and then put in storage. They are reasonably fresh 1985 7591A tubes. They all test strong on the Hickok 6000 tube test and all show low grid 1 leakage.Absolutely, it depends on the specific tubes and you're right most tube testers will not reveal bias weakness. Most testers apply around 150-180v and are not adequate for real operating conditions like 400v to the plate.
Are your 7591As new production like Tung-Sols or Electro-Harmonix?
Brilliant. I really like what you did mounting the test points and trim pots topside where they can easily be adjusted....Its really handy to have your power tube bias adjustments above board vs inside the chassis....
Thank you! I'll find it i'm sure.Josey,
Here is a schematic for a 500C with IBAM and some other mods. The 500B is similar enough so I built my IBAM as shown in the schematic
Edit: I can't figure out how to put the schematic here.
It's in the AK Database.
Nice work Matt....And this is where I mounted it - just made one of the transformer studs long and mounted it between two nuts.
View attachment 1329756
I can build you one of these, but it will cost you, and it's not very easy to deal with replacing the can cap.
View attachment 1329758
This looks pretty great. I'm not sure which one to go with. This may sound like a dumb question but the can cap that was there, where did it go or does the IBAM replace the can cap? I know I sound stupid here. And enjoy Florida! Thanks.Josey,
I have all the parts on hand to build you a board, so no worry about funds yet - I think shipping will be more than parts. I am going to Florida for Thanksgiving, so it will be after that that I finish it.
Here is the formula I used (Bruce deserves a lot of credit for making the instructions clear enough that I could figure it out without having to ask a bunch of questions) -same parts too: http://audiokarma.org/forums/index.php?threads/show-me-your-ibam-ibba-2016.713900/
And this is where I mounted it - just made one of the transformer studs long and mounted it between two nuts.
View attachment 1329756
I can build you one of these, but it will cost you, and it's not very easy to deal with replacing the can cap.
View attachment 1329758
Does anyone have any advice on how not to become obsessed with this? I'm already brainstorming a whole vintage audio equipment testing restoration with Oscilloscope, Tube tester and a tube multimeter prior to my 500-B restoration. LOL.