11-11-2013, 11:14 AM
A few answers:
2. Most caps are filter/decoupling so standard values of 0.01uF, 0.022uF and such are good replacements, and are readily available from Mouser or anyone else. I buy polyester films.
For looks I stuff them inside old paper tubes but this is up to you.
Do not touch mica caps, they are likely OK.
3. Large caps of more than 1uF are probably electrolytics and can be, with appropriate voltage rating, changed for today's electrolytics. Again, many of us stuff old tubes with new ones, for look and feel thing.
If it is the rectifier filter (the one right after the rectifier tube) it is desirable (many folks do not pay attention to that) to have your ripple current rating correct. I usually go with at least twice the load current.
5. Safety: if your radio has the Mains power transformer you do not need the isolation transformer. Unless you operate it on the bare concrete floor in the basement or outside - then it is desirable. Also you could possibly add (only for those with mains transformer - NOT FOR AA5s) Earth wire to the chassis, to make it safer in case the transformer breaks down.
This will also serve as the Ground that was connected separately before (if it was connected - often it was not).
Fuses: I usually go with a slow-blow about 1.5-2x rating vs. the radio consumption but no less than 1A, so if it draws say about 1A from the Mains (for a large powerful radio of 100-120W total power) use a 1.5-2A slow-blow fuse.
And remember - the fuse is not there to save the device - it is to save your house from the device if it decides to go up in flames. A short circuit will surely exceed 2A many-fold. However the fast-blows need higher rating as they may be quick to react when the inrush happens; it is a well-known phenomenon when old radio fuses burn on turn-on without anything being wrong with the radio - this is how large transformers operate.
2. Most caps are filter/decoupling so standard values of 0.01uF, 0.022uF and such are good replacements, and are readily available from Mouser or anyone else. I buy polyester films.
For looks I stuff them inside old paper tubes but this is up to you.
Do not touch mica caps, they are likely OK.
3. Large caps of more than 1uF are probably electrolytics and can be, with appropriate voltage rating, changed for today's electrolytics. Again, many of us stuff old tubes with new ones, for look and feel thing.
If it is the rectifier filter (the one right after the rectifier tube) it is desirable (many folks do not pay attention to that) to have your ripple current rating correct. I usually go with at least twice the load current.
5. Safety: if your radio has the Mains power transformer you do not need the isolation transformer. Unless you operate it on the bare concrete floor in the basement or outside - then it is desirable. Also you could possibly add (only for those with mains transformer - NOT FOR AA5s) Earth wire to the chassis, to make it safer in case the transformer breaks down.
This will also serve as the Ground that was connected separately before (if it was connected - often it was not).
Fuses: I usually go with a slow-blow about 1.5-2x rating vs. the radio consumption but no less than 1A, so if it draws say about 1A from the Mains (for a large powerful radio of 100-120W total power) use a 1.5-2A slow-blow fuse.
And remember - the fuse is not there to save the device - it is to save your house from the device if it decides to go up in flames. A short circuit will surely exceed 2A many-fold. However the fast-blows need higher rating as they may be quick to react when the inrush happens; it is a well-known phenomenon when old radio fuses burn on turn-on without anything being wrong with the radio - this is how large transformers operate.
