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Citation V clone rebuild

RickB said:
Well, the biggest thing is that they make tubes last longer...back in the fifties the JAN testing proved that reducing a tubes envelope temp had a great effect on increasing tube life, my Collins R-390/URR and R-390A/URR are just filled with tubes and were expected to be on duty 24/7/365, and the IERC tube shield were developed for just such instances.

I do not find any sound degradation with the Pearls installed, and if it ends up costing me a lot less for tube replacement, especially the NOS tubes in the front end of my MC240, or the replacement tubes for the Audible, then it's a good thing...

And no, I have nothing to do financially with Pearl, I'm just a very satisfied owner.

I am also observant of the fact that the entire amplifier runs cooler, whether it's my VTA-70i or the 240, and the room doesn't get as warm....it radiates the heat from the unit more efficiently before heating the entire unit warm up to higher temps...my digital IR thermometer confirms that the chassis even runs much cooler when the power and input tube temps are brought down...kind of like back in the day putting a better radiator in a hot rod along with an external oil cooler helped keep the engine cooler even in 100+ degree weather here in Texas....been there, done that.
Click to expand...
Thanks for that
Makes a lot of sense
I use a fan after the power transformer warms up
Pearls don’t need to be plugged in
Bobhorn
 
Ok, I guess I'm convinced to at least clean up and paint the chassis if not buy/build a new one. I will need to remove so much of the the stuff in this chassis that I may as well go all the way. More inclined to buy/build a new chassis but it will delay the finish a bit.
Thanks a lot folks,
John
 
If you do, I'd consider an arrangement where the power transformer is mounted on one end of the chassis rather than in the middle - particularly if the power transformer doesn't have a hum strap. When in the middle, it places each amplifier at opposite ends of the power transformer's magnetic field, which induces a hum voltage in the ground circuit between the two channels, and particularly so when the input jacks appear at each end of the chassis. In that configuration, when the interconnects are plugged in, and their ground connections are shorted together at the preamp end of the interconnects, a ground current flows in the interconnects causing hum. Using aluminum or other non-magnetic material for the chassis will keep most such noise at bay with such a layout, but a best practice layout will have the power transformer at one end of the chassis, and the inputs at the other end. You might see my thread here regarding a dickens of a time I had in dealing with this very issue in a Heathkit AA-30 Amplifier, where in the power transformer is located in the middle of a steel chassis, and the inputs are located at each end:

https://www.audiokarma.org/forums/i...e-rough-polishing-heaths-aa-30-aa-111.663199/

A middle mount works OK with proper attention to the amplifier circuit layout (ST-70 is an excellent example of a great middle mount layout), and even works OK with the inputs at each end (as in the ST-35) if the amplifier circuit layout is given proper attention. Just food for thought if you start fresh!

Dave
 
Thanks Dave. I remember reading that Heathkit writeup. I was originally planning to restore this unit electrically and enjoy it but all of the comments have me thinking about a remake of the chassis or a new chassis. Not sure what I will do now.
John
 
I've done a number of amps with the PT in the middle- but I always put BOTH input jacks right next to each other, on one end of the chassis, and wire the ground terminals of both jacks together, as well, no matter where the PT is located. That eliminates the ground loop in the interconnects- regardless of what induced current there may or may not be in the chassis.

That said- having the PT on one end, is likely one reason why the Magnavox amps can get away with grounding everything directly to the chassis next to each component group, without having excessive background hum. It's a VERY good thing to put the PT in one corner, if the ground isn't a star with a single chassis connection, for sure...

IME, one of the other is usually sufficient, though- one single ground to the chassis at one single location, or putting the PT in a corner. Both have worked great for me.


Regards,
Gordon.
 
I've been hiding under a rock again. Just saw this thread. I've done a few projects like this one. Agree with putting the PT in one corner. No worries about how long it takes. The current amp I'm building has been about 9 months from inception of the idea to a working amp I can listen to. It's better not to rush it because you want the amp to be the best it can be when done, and in say 5 years you won't remember how long it took to build anyway. Personally I would take the time to finish the chassis as best you can. You'll be glad you did years down the road. My opinion anyway.

The other thing I learned in building a few like this is to well test each phase before moving to the next. It saves headache and rework later. I'll be following along with this one.
 
kward said:
I've been hiding under a rock again. Just saw this thread. I've done a few projects like this one. Agree with putting the PT in one corner. No worries about how long it takes. The current amp I'm building has been about 9 months from inception of the idea to a working amp I can listen to. It's better not to rush it because you want the amp to be the best it can be when done, and in say 5 years you won't remember how long it took to build anyway. Personally I would take the time to finish the chassis as best you can. You'll be glad you did years down the road. My opinion anyway.

The other thing I learned in building a few like this is to well test each phase before moving to the next. It saves headache and rework later. I'll be following along with this one.
Click to expand...
Did Kegger ever document a Citation 5 rebuild?
 
I have Citation 5 in pieces all painted up waiting for wiring work... Is your B+ going to be too high for the JJ caps? When it was running, I remember around 500dcv at start up...I've had good luck with the JJ caps, but I don't know if they have a safety margin? Thx for taking the time to show your build..
 
Crispy,
I don't have an absolute answer to your question but I'm glad you asked as it reminds me that I forgot the inrush limiters. I always seem to need to rework something when I build.
John
 
In rush limiter will help. I've been using 600vdc electro's from "justradios.com" in high voltage pwr supplies. No relation to company. Makes assemble easier & the price is ok.... Really looking forward to your build...
 
I'm considering a new and larger chassis. Since I will be using new production 6L6GC from Jim McShane, any comments on using a pair of 6CJ3 damper diodes to reduce the B+ a bit and still have a fairly still and quiet power supply? Just something that occurred to me since I use them in my current DIY amp.
Thanks,
John
 
Well, this project keeps getting bigger. I started to replace some out of spec resistors on the turret boards and discovered that the turrets are very poorly staked. Many are loose and cracked at the staked flare. I think I should just build new boards if I'm going to continue with this project. At this point I think all I really have is a transformer set.

Any cool ideas on what I might build with the transformers if I don't just copy the Citation V circuit? I would probably want to use the power supply since I have already rebuilt it.
John
 
nerdorama said:
Well, this project keeps getting bigger. I started to replace some out of spec resistors on the turret boards and discovered that the turrets are very poorly staked. Many are loose and cracked at the staked flare. I think I should just build new boards if I'm going to continue with this project. At this point I think all I really have is a transformer set.

Any cool ideas on what I might build with the transformers if I don't just copy the Citation V circuit? I would probably want to use the power supply since I have already rebuilt it.
John
Click to expand...
So did you use the McShane spec values or Stock Citation 5 values? For the power Supply?
Staying with the homebuilt chassis?
Bobhorn
I’m following your build as my Citation 5 Rebuilt by Ed Duda is out of commission!
Bobhorn
 
I used Jim McShane's scheme but sourced the parts mainly from Mouser. I'm considering making new turret boards. I can buy a basic turret board with two rows of preinstalled turrets and then add the extra turrets in the middle region of the board to clone the boards in the amp and it won't cost too much to do it. BUT, there are many options open to me since the circuits need rebuilding anyway. I have some Baby Huey PCB's from DIYaudio and I think I'll study the requirements and see if these might be a good alternative. Guess I'll head to the taproom to think it over.
John
 
nerdorama said:
Any cool ideas on what I might build with the transformers if I don't just copy the Citation V circuit?
Click to expand...
What is the primary impedance of these output transformers? I'm assuming about 6K since the Citation V used 7581s?
 
Ah that’s a rather good match for a triode push pull output stage. Done right, I bet that would make for a really nice sounding amp with those output transformers. You could do something “normal” like using KT66’s or 807’s or the 12V counterpart the 1625. Or you could go more exotic with the 6AV5 like what I did in my triode amp. If you want something really “out there,” maybe the 38HE7. (They might still be on the dollar menu at ESRC.)

I think you are forging your own steel if you build around the 38HE7 though.
 
I thought about using triode connected tubes of some sort. I have a quad of new 6L6 Tung Sol's I bought from Jim McShane for this amp. I also have a good handful of Russian GU-50's which are supposed to be somewhat like a 300b when triode connected. If I go triode I would probably want to go class A without global feedback or possibly pentode with local feedback. Either way, class A would need a lower B+ than the HK uses. Not sure what to do now since there are so many options. After thinking myself in circles I will probably just build new turret boards and make a Citation V.

Appreciate the thoughts and suggestions.
John
 
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