Harmon Kardon Citation V PS rebuild time

[Coffee Phil]

The electrolytic capacitors in my Citation are at end of life. One has failed and most of the rest have lost about 1/3rd of their capacatance.

The old twist-lock caps are virtually impossable to get. NOS is probably not the first choice with electrolytics. There are some being made today but they are silly expensive.

This amplifier is becoming collectable so keeping it looking OEM has some value. Mine is no garage queen, it gets fairly heavy use.

Since getting new twist-locks looks like it will cost more than 1/2 of what decent Citation 5s are going for on eBay I probably won't be doing that. The two options which I am now considering are Jim McShane's kit and one from a guy named Sheldon Stokes. http://www.quadesl.com/refurb/refurb_hkCitation5.html

Jim of course is regarded the Harmon Kardon Guru and his kit includes computer grade caps with mounting clamps. In Jim's kit the first stage of the filter is increased to a whopping 400 microfarads vs. Sheldon's 235 microfarads. This stage supplies the anodes of the final stages so the extra energy storage is appealing. In the following stages Jim's kit offers 100 microfarads vs. Sheldon's 235 microfarads.

In Jim's kit there are more capacitor cans than in the OEM setup and I haven't seen a picture of the installed kit. Sheldon's kit uses a circuit card with PC mount capacators. The installed picture he provides looks very sanitary although not like 1960 electronics.

One other difference is that Jim does not provide bias adjustment for the output tubes and Sheldon's board has a home for the bias adjustment pots. In an earlier freshening up of this amp I felt the need for the bias adjustment and RTVed bias pots to the ballance pots. It works and doesn't look too bad but in the light of what this amp is now worth I'll want to refine that a bit. Sheldon's kit will do that.

Any Thoughts? Also are there any more kits out there which I should consider?

Of course I could search out the parts my self and likely save some money, but even as an old retired guy the time would be more than either of them are getting. The price is similar for either Sheldon's or Jim's. Jim gets about $100 and Sheldon sells the board for ~$50 and he provides a BOM with Mauser's part numbers and prices. The parts cost to stuff the board is about $50.

Phil

[Coffee Phil]

I pulled the trigger on the Sheldon Stokes board and I am about to order the parts to stuff it.

Jim did provide a link to a picture with his kit installed. It looked pretty clean, but I think Sheldon's approach looks a bit more tidy. That and the home for the bias adjustment pots on board swayed my decision. Jim does not like PC boards in Citation tube amps. I am not sure why he feels that way. It could be purely astetic (perfectly valid) or experience with vacuum tube equipment in the 50s when circuit boards were starting to appear. Back then consumer electronics used phonelic boards and they even mounted power tube sockets on them. In the day I used to repair consumer electronics and I became "circuit board phobic". Today I think FR4 board used with common sense is just fine.

One big advantage Jim's kit has is more energy storage in the first stage of the PS filter which feeds the final stage anodes. He has 400 microfarads vs. Sheldon's 235 microfarads. I am going to order extra electrolytics so if I feel the need for more capacitance in the first stage. I can just cut up some glass epoxy board and mount the extra caps on it. I will have the option to put the caps as a aggragate in parallel with the existing first stage caps not allowing them to be part of the doubler if the rectifier peak current scares me, or emulating Jim's approach if I want higher B+ voltage and possibly better power supply regulation. I may try it both ways.

Phil

[Coffee Phil]

Here is a picture of the bottom of the amp showing the capacitors to be replaced before the bulk of the "demolition":

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The power supply filter resistors have been removed to enable checking the electrolytic caps. The blue caps were replaced before I acquired this amp in the mid 70s. They are part of the voltage doubler. One is essentually open. One output tube had an open heater and the anode pin of the socket in an output tube in the other channel was broken so the amp was running single ended in both channels.
The remarkable thing is even with all this stuff other than a bit of hum this amp didn't sound all that bad.

Phil

[Coffee Phil]

The Sheldon Stokes board arrived yesterday and the parts to stuff it just came.
I have a few tests of the existing bias supply, some of which I want to keep, then I start the "demolation" of the old power supply filter and construction the new one.



Phil

[Coffee Phil]

I believe I have all the parts which I need to complete this project now.

As I said Sheldon Stokes approach won out mostly because of the bias adjust pots but I liked the energy storage in Jim Mcshanes approach. Here is my modified Sheldon Stokes board with the home for the extra caps:



Hopefully I'll be hearing my Citation V soon.

Phil

[Coffee Phil]

The board is stuffed and Humisealed:

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Below is the trace side:
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I did not stuff the rectifier diode in the bias supply. Sheldon Stokes likes to stick with the original designers circuit topology. During a previous re-freshening I had replaced the selenium bias rectifier with a silicon bridge. I want to retain the bridge so I am trying to figure a sanitary way to mount it.

Phil

[crofk]

Looks nice cf. I'd like to find one for a Marantz 8b. I don't know of any on the market though.
Keep us posted on your progess.

kc

[Coffee Phil]

Hi KC,

Thanks. I am looking at two bridge rectifiers, one surface mount and one leaded which have ratings which are sufficient. The goal today is to decide and mount the one which I decide on.

I looked at Sheldon Stoke's site. Sure enough he doesn't offer anything for you Marantz. I did find this outfit: http://www.vacuumtube.com/products.htm
They seem to have something. I don't know if it includes a board or how sanitary it is. They don't have a picture of it. You might call and see if they wiil describe it or send you a picture.

Phil

Looks nice cf. I'd like to find one for a Marantz 8b. I don't know of any on the market though.
Keep us posted on your progess.

kc

[Coffee Phil]

I decided on the leaded bridge. Here is the part on the Sheldon Stokes board:

[img][/img]

Not as sanatary as if it were included in the layout but acceptable to me. I connected the bias winding of the power transformer to it and measured voltages. It seems to work fine.

Phil

[crofk]

Thanks cf, I'll give it a looking at.
It appears that your project is coming along nicely. I would bet you notice a big difference when finished.

kc

[Coffee Phil]

At long last the Citation 5 is back in service.

Below are some pictures of the amp with the modified Sheldon Stokes power supply board:

The first is a shot under the amp showing the new electrolytic caps and the board.

[img][/img]
The little strip of aluminum sticking out from under (actually over)the caps is a heat shield for the first decoupling resistor. I was afraid heat from it would degrade the insulation on the ~50 year old wiring.

Next is a shot showing the top of the chassis.
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The 5881 tube are new Sovteks. I like the look of them with plastic showing only on the bottom. I don't recall paying for matching but they seem well matched. I bought all new tubes but only used the 5881s. The new 12BY7s are OK NOS RCAs but the old ones (also RCAs) were still good so I left them. The new 6CG7s used in the phase inverter were crud so I left the old ones. The two triode sections were very poorly matched. I guess that the former Yugoslavia, or at least Elektronska, was not very good at tubes.

Below is another shot showing the offending tube and its carton.

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Below is the amp ready to go back in service.

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Below is the Citation 5 in place doing what it does. The big "sand" based amp to the right of the Citation is an Adcom 5400 used to drive the subwoofers.

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Soon hopefully I'll have the Citation's companion piece, the Citation 4 preamp, sorted out. By the way its panel needs to be re-silkscreened. Any suggestion of someone skilled in this who won't require me to get a mortgage on my house would be appreciated.

Phil

[Bran Kulez]

Good project and nice job!

[Bran Kulez]

btw, considering your efforts, shouldn't it have a slightly more prominent position than on the floor?...

[Coffee Phil]

Hi Branku62,

Thanks for the complement on my work.

I agree that Stewart Hegman's design deserves to be better displayed. I have received a new to me equipment cabinet and more is to come. The plan is for the Citation to reside on top of one of the cabinets where it will get all of the air it needs and will be in plain sight. So far my wife has raised no objections.

Phil

btw, considering your efforts, shouldn't it have a slightly more prominent position than on the floor?...