how to value Fisher preamp

I have a Fisher 400-cx-2 in the walnut case, 100% original, never touched and is 100% working condition. It is part of my dad's system that he assembled in the early sixties. He was always very fussy about it and and it shows. He passed many years ago, and mom feels like it is time to sell it off, but we need to get some ides about price and if anything needs to be serviced. There is also a Fisher KM-60 tuner in the walnut cab that works perfectly, stereo beam and all.
Two of the knob trim covers (gold)are off(one missing), but the knobs are still intact. I am wondering about finding the knob cover and if they can be re-glued?
Do vintage pieces like this need to be re-tubed, or if working well just put up for sale, and how does that affect value? Any input is helpful.
If you are looking for more than $10 at a garage sale, then these units should definitely be serviced before being put up for sale. The service person should have a good idea of the value of the piece.
That's just my opinion. I know I would not shell out what some folks will pay for vintage units without some form of service documentation. I might take a flyer on something at a yard sale w/o documentation, but if you think it's worth more money, it will be up to you to provide the proof.
This always seems a strange question. The inevitable answer is, it's worth what someone is prepared to pay for it, at the time. That is the advantage of an auction, whether on this site or E-bay. Providing you give a longish period to generate interest and there are at least 2 interested parties, it should find the best price at that time.

A lot of the problems with "expert valuation", is that the expert is'nt buying the item. The price will vary, it depends how many are on the look out for the item at any one time.
Leave them in completely stock condition. Do not attempt any repairs or mods. The value of the units depends upon them being stock and in excellent cosmetic condition. The brass knob inserts are not important, but discoloration of the front panel metal is. The preamp is far more valuable, you could get $1,300 - 2,000. There is one on ebay right now for $2,500. I think it is over priced, but you should follow the sale. The tuner is worth $150 - 300.
I am in general agreement with the comments by David and Onhwy61. However, in order to have a reasonable chance of realizing anything like the prices that were mentioned, I think that your ad would have to indicate a willingness to sell and ship to international bidders or buyers. And even if you do so, it is conceivable to me that depending on the luck of the draw you could realize far less than those prices.

If you were to first have the pieces professionally serviced, chances are that what would be done would be mainly testing of the tubes and replacement as necessary; replacement of electrolytic capacitors; lubrication of controls; and "alignment" of the tuner circuits. Many of the people who would be interested in this kind of equipment are capable of doing that themselves, and IMO chances are that the cost of professional servicing and the likely sacrifice of originality would outweigh the possible benefit.

Fisher made good products in those days, and these particular models are no exception. However, they are not among the most highly sought after Fisher models. FYI, some older literature I have indicates that these models were made from 1964 to 1968, and originally sold for $200 for the 400CX preamp (I don't see a listing for the 400CX-2), and $170 for the tuner. Those were neither particularly high nor particularly low prices in those days for components from the better manufacturers. The tuner was apparently a kit, assembled by the purchaser.

-- Al
I think you would be better off having these Fisher pieces brought back to spec by a very highly regarded restorer. The Fisher Doc is famous and will make it worth more IMO. I am a bit ambivalent as a true collector usually wants rare pieces left entirely original. So you have to bet on whether there will more interest from practical users of old gear like myself (who is using a Fisher 400 right now) or the purest collector.
Having the units updated will risk shipping damage back and forth to the servicer and can take from 3 to 9 months to complete. It probably will not increase the value to a collector. Practical users will not pay as much as collectors anyway. It is a questionable way to spend $500 to 1,000.
Fair enough Ohnwy61, that makes sense.
Mechans have you evaluated the phono stage on your 400? Im playing with it now and have some mixed feelings....