Fender Bassman 100 rebuild

[Mark]

Thanks for the replies and advice. The Hammond 1650TA is very similar in dimensions to the original transformer AFAIK. This was suggested offline by a friend who has one. The core width of the WA appears to be similar to the 022889 transformer.

https://www.hammfg.com/part/1650TA?referer=1047

Regarding thoughts about the amp. I suspect it fell on hard times once the output transformer blew and received the 022889 output transformer. It was then treated as one of those useless silver faced amps. I had wondered if a guy owned both and preferred the sound of the larger output transformer?
I'm not sure that is likely though.

[Mark]

Cleaning up sockets.

IMG_1288.JPG

[pompeiisneaks]

The one with the brown poopy stuff is clean? right?

~Phil

[Mark]

Not quite Phil. That poopy stuff is still thinly on the sockets. I need to soak them for a bit.

[fredfretter]

Don't know what your using to clean, but I found CRC electronic cleaner 05103 very good for cleaning flux when I get
through soldering. The older deposits may take more effort.

[Mark]

I'll keep my eye out for that CRC product. I'm cleaning the chassis today with wax and grease remover. It works okay, but alcohol is better.

[Mark]

The replacement Hammond transformer turned up today. It makes the Schumacher 022889 look like an output transformer for a Champ.

IMG_1291.JPG

The holes look like they will line up and it clears the choke which is good. It makes me wonder if the power transformer will be up to the task.

Here is a picture of the original transformer from tonegeek.



There is a bit of rubber between the transformer and the chassis, I wonder why Fender needed this?

[Mark]

Awaiting components is a hassle, as I now have time. This is it do far.

IMG_1294.JPG

[Mark]

Another thought I've had is to increase the grid stoppers on the output valves from 1.5K to 5.6K.
The thoughts behind this is in undistorted operation there will be no difference in treble response, but when the output valves go into forward conduction the resistors will slow the current flow down a little and less high frequencies will be generated thus the distortion will be bass friendly.

Is this a reasonable idea, or is it rubbish?

http://www.valvewizard.co.uk/gridstopper.html

Not much info on output valves here.

[Mark]

One day whilst listening to Charlie Wilson play Baja, I googled The Blue Hawaiians, here is the link.

https://en.m.wikipedia.org/wiki/The_Blue_Hawaiians

[pompeiisneaks]

Another thought I've had is to increase the grid stoppers on the output valves from 1.5K to 5.6K.
The thoughts behind this is in undistorted operation there will be no difference in treble response, but when the output valves go into forward conduction the resistors will slow the current flow down a little and less high frequencies will be generated thus the distortion will be bass friendly.

Is this a reasonable idea, or is it rubbish?

http://www.valvewizard.co.uk/gridstopper.html

Not much info on output valves here.

I saw a discussion about grid stoppers on another thread, I somehow missed this question. I think the point was increasing them won't impact the tone at all until you get a lot higher like order of 100k or so, and adding more is always better until you impact the tone a bit. in other words 5.6 is often used in other amps I've seen and from that thread it sounded like it's a win/win. It wont' hurt and it can and usually does help with things like oscillations etc.

~Phil

[Mark]

Thanks for your reply Phil. I thought it was reasonable to increase the grid stoppers.

Jelle Welagen convinced me to use the stock value and use a mosfet follower. I'll build the amp up first and then see if it needs the mosfet follower. No point making things hard on yourself.

[Mark]

I've had parts arrive from C.E.Distribution and I'm back in the saddle again. As previously stated, I'm running 110uF for the first stage, 47uF for the screen grids and the regular 22uF caps from there. Hopefully, this will result in the amp being able to deliver a good bass response.

IMG_1349.JPG

[Mark]

IMG_1371.JPG

[amidzadado]

Very nice...