Installing the Fisher Doc or other upgrades in the Fisher tube gear is not very difficult if you have ever done any soldering of electronics.
You will need a decent soldering pen, not a soldering gun, of 25 to 40 watts, with a long narrow tip to be able to reach some of the solder connections.
A digital multimeter to help check continuity of your solder connections. Even an inexpensive one will work for this.
You need to be able to minimally read a schematic diagram, to follow some of the circuit wiring that leads to the parts that must be replaced. Most of the parts are readily located, a few will try your patience as you hunt around for them in the circuit wiring.
When you remove the bottom cover, you will be working around electrolytic capacitors and coupling capacitors that store high voltage (450 volt) charges. Before beginning work, unplug the unit. Be sure these have been discharged.
To be sure the capacitors have been discharged, do this yourself with a pair of wire leads with clips, a 100 ohm 5 watt resistor or similar, connnected to a small screwdriver. Ground one lead wire to the chassis and connect the other end of the lead to one side of the resistor, the other lead goes from the other side of the resistor to the screwdriver shaft. Briefly touch all capacitor leads with the screwdriver, for a few seconds. Be sure to get the hot leads of the multi-section capacitors. Touch everything twice, just to be sure. Now you can safely work inside the chassis with no danger of getting shocked.
The restoration tasks are broken down into logical steps. Approach each one as a separate upgrade, and don't try and do it all in one session.
Resistors are not polarized, it does not matter which way they are installed, end to end. Diodes, rectifiers, and most electolytic capacitors and some other capacitor types are polarized. You absolutely have to know which is the + and which is - on these components before your install them in their correct locations.
Failure to properly orient one of these polarized components will result in destroying the component, they may even explode, and may further damage other parts of the unit. Be sure you know what you are doing, double check if you have any doubt before proceeding.
The best way to learn is by example. If possible, get a good look at the inside of a similar Fisher unit that has been restored, so you can see where the affected parts are inside the chassis. If one is not available, then try and get some digital photos with suitable closeups to see the parts before and after installation.
Check out Phil's Old Radios site. He has generously provided some good photos of the various stages of restoration he performed on a Fisher 800B receiver. The details for a Fisher 400 or 500C will be slightly different, but you can get a pretty good idea of where the various parts reside and what this looks like once the parts have been replaced. Go to the Radio Directory, and under the letter "F" you will find Phil's aricles on restoring the Fisher 400 and 800B. He provides really good photos on installing various needed upgrades in the 800B article.
http://antiqueradio.org/index.html
As you will be able to see from Phil's photos, these Fisher units use point-to-point wiring for most connections, generally no printed circuit (PC) boards. This is actually easier to work with and more forgiving than soldering on PC board.
Vintage Dynaco tube gear, in comparison, have PC boards that were pretty flimsy when new and have become even more fragile with age. Also, these units have fragile solid core wiring and the PC boards have very thin solder traces that can easily be damaged. So unless you are replacing all of the PC boards and wiring in a Dynaco PAS preamp or ST-70 power amp, attempting any more soldering on these old boards than absolutely necessary is not recommended for the novice.
I'm not sure why you would want to use a PAS preamp, as it has not provision to drive headphones. The PAS-2 or PAS-3 preamp coupled with the ST-35 or ST-70 power amp would be an interesting headphone amplifier combination.
The Dynaco SCA-35 is an all-tube integrated amplifier that uses 12AX7 for the phono stage preamp, 7199 driver tubes, and a quad of EL84 (6BQ5) power tubes for 17 watts per channel into 8 or 16 ohms. I recently purchased a Dynaco SCA-35 to see how it would perform as a headphone amplifier. I will post an update when I have received this item and have a chance to try it out with various headphones. The SCA-35 did not come with a headphone jack, but there is a mounting hole in the rear of the chassis to install one, and the assembly guide/owners manual details how this should be done.
