1) Loose the two Chocolate Drop Caps in my Bassman? As you cqan see, any replacement would have to be radial caps. I bought two 6PS Orange drops, that were supposed to be NOS, however4 they do not look like the old ones.
2) If I put 2K screen resistors ( right now I have 5K ), would that be low enough value to fuse in the event of a tube failure?
I know the subject of fusing in intricate, and that some do not believe in using the the screen resistors as fuses, but I don't want to ever blow up my transformers if a bad cheap tube blows
Unless they're leaky or physically damaged, you shouldn't have to replace the coupling caps. Power supply electrolytics are a different story, as they have a limited service life and will eventually dry up and die.
As for the screen resistors, do you mean the screen stoppers or the screen dropping resistor in the PS rail? You should be safe using a 2K screen stopper, as most original Fenders used 470R resistors here, if they used them at all. Decreasing the screen dropping resistor will increase the voltage on the screen grids, which may or may not be advisable. Proceed with caution if that's the case, but it depends on what your end goal is.
why do choc drop replacements have to be radial? in any case I use lots of Mallory 150 film caps, get nice clear tones. Available at Antique/CE, Mojo, Mouser, & more, & reasonably priced.
You have 5K screen resistors? Must be well compressed when you start to wail. I don't much count on SG resistors to save the transformer(s) in case of an output tube short. You could follow Marshall's lead and put in an HT fuse 500 mA, if that would ease your mind any. Fender bassman transformers are pretty tough and rarely fail anyway so let 'er rip, tater chip.
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Now that the photos popped up - she looks like a good 'un! Mostly old blue Mallory film caps anyway. If you insist on swapping out choc drop caps those OD's look OK to me.
in my experience the coupling caps should be replaced with time - depends on how much use the amp has had. If you want the amp to sound as new, replace them. You'll find that the amp has a lot more bottom end than it used to.
Also, those chocolate style caps in old fender amps tend to sound pretty bad. I would hang on to them, in case you ever want the amp to be stock again - but try replacing them and see what happens!
Regarding the 2K and 5K screen resistors that Jerry2013 refers to, from the context, my reading is that he means 2 watt and 5 watt, ie the power rating rather than the actual resistance value.
My view is that unless other mitigation for tube failure is implemented (eg B+ fusing) the original 470 ohm 1 watt spec for screen grid resistors remains the best option.
However, given materials advances and the collateral damage that carbon based resistor types can cause when heavily overloaded, metal oxide types with a flame retardant coating should be used.
Pete
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
See the 2nd photo, has a largish radial cap been used on the bias board?
It looks like it's standing up and unsupported, other than by its leads, which are likely bent at 90 degrees close to the cap body.
I don't perceive this to be good practice, especially for such a 'mission critical' part as the bias supply cap.
I hope that there is some sort of additional mechanical support for the cap, that is not apparent in the photo.
Pete
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
Last year my son brought home a '72 SF Bassman 10 that belonged to a friend. Supposedly his band had landed a record contract and planned to take it touring and wanted a "tune-up."
Here are some before and after pictures of the work. It lasted the road trip and is still working. I never did get paid.
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I agree with pdf64 on the screen resistors. A fused HT would be best but without I'll stick with the screen resistor fuse. 470 sounds best to me on the 6l6, 2 or 5k would way too compressed. Esthetically I would use an axial bias cap (100/100) but probably not an issue with the radial one. I've been known to use whatchagot engineering.
I just rebuilt a 66' ab165 bassman. Those brown turds sounded and tested fine. I used to think they had to go, but I've
Been leaving in the last few years and they sound fine, ugly though.
Fender seems to put them in certain places
Almost always right at the pi, so maybe they had a purpose.
I rebuilt a bandmaster rev head that had a full complement of brown turds and skinny plastic wire, it was
One of the better sounding amps which surprised me.
