1964 Vox AC10 just purchased trying to remove RF interference

[echo44]

I just bought a vintage Vox AC10 on impulse.(paid way too much
The amp cosmetically looks clean as a whistle. Inside some of the electrolytics have been replaced everything else is original including the speakers. Almost looks like it has never been used.
the amp is a little noisy and I am picking up some radio stations and unfortunately the music selection is not that great.
Using a better guitar cable helps and the radio station volume changes when I touch the metal component of end of the guitar cable. When teh cable is not plugged in and the volume is cranked no radio station. Tubes are slightly microphonic especially when tapping the vibrato knob control.

few questions:
1) would placing a .01 uf cap between the ring connection in the jack to the chassis help as there are 4 inputs I would need 4 caps? I added a ferrite collar around the power cord near the entrance to the amp that didn't seem to help. was also recommended placing a 47pF cap between ring and sleeve see my post below as I am editing this. Also chatGpt suggested another mod see post response below.
2) the tubes are not shielded on this amp would wrapping tin foil around them help or just shorten the life of the tubes from heat. Or any better ideas?
3) the original wiring to the speakers seems very flimsy the wires connect to the transformer through a little terminal board. It is surprising how thin the wires are to the speakers
if I change the wire to thicker wire will it decrease value of the amp?
4) the speakers are the originals, they seem to function well although given their age might a new pair of 10" alnico sound better such as the Celestian G10 gold 16ohm? Plus this would allow me to remove the speakers and store them to protect them in case I sell the amp someday.
Overall, I am having some buyers remorse as the amp was $$$ as it was so clean. I did not get a chance to play it much before buying it. The amp seems a little "closed" sounding if that makes any sense? I have a vintage 1972 Princeton I was comparing it with and I know it's a whole different ball game but the Vox seemed a little less open sounding? Definitely a more compressed sound. This is my first Vox I was looking for a vintage ac-30 yet found this and didn't want to miss the chance to own a vintage Vox

Any other suggestions welcome!

[Stevem]

If the wires off of the input jacks are not sheided then that should be the first action done to kill the radio receiver effect.

The sheild should only get grounded at the input jack side and shrink tubing used to close off the other side.

There's also a easy resistor and cap mod you can add to the jack to shunt radio frequencies to ground.

I can't recall what values I used the last time, but later at home I will review my notes and make another post .

That 18 gauge speaker wire is more then enough for a10 watt amp.

The AC 10 has a cathode biased output stage and the Princeton does not so that makes for a change in feel as the amp gets played louder.

The boxy sound is due to those speakers, so like you have said, remove them and store them safely.

The compressed sound you speak of is mainly due to those Alnico magnetic speakers, as that's what Alnico does once they are driven hard enough, but on the other side of the coin that compression also provides sustaine so you need to decide what you want more or less of as the amp gets played louder.

Also that dinky output transformer will compress as the amp gets dined.

When you go shopping for new speakers be sure that there SPL rating is above 94 DB.

A ciramic and Alnico mag combo of speakers in these amps works out great, but Alnico magnet drivers are always pricey so be forewarned!

It also helps to line the wood walls of the cabinet with sound absorbent material, as this will help the drivers to react as if the cab was bigger.

[martin manning]

Make sure all grounds are good, including all hacks and pots have clean and solid connection to the chassis. Many times simply tightening all pots and jacks can eliminate a lot of noise. The other prime suspects are carbon comp resistors, especially plate loads.

[echo44]

So I tried to tackle the noise issue with help from ChatGpt?
Chat GPT had me put a 47pF cap between the sleeve and ring lugs for the input jacks. I tried it in 2 and had no effect.
When I plug a guitar cable into one of the jacks the radio station plays on either channel including the one channel that doesn't currently have the guitar cable. When I remove the cable all radio noise stops at any volume. ChatGPT says that's because of the type of input jacks released a spring when the cable is removed essentially grounding everything. The amp without a guitar cable plugged in is not that noisy and no radio station Rf, I thin this means it is not related to the carbon resistors failing?

ChatGpt states the RF interference is probably entering down the line. Is now recommending I add a "grid stop resistor at the .01 uF turret to V1 and add grid shunt cap solder 1nF cap from the grid post to the chassis?

Has anyone have familiarity with this mod? Will this affect tone ChatGpt says no?

The cables going to the input jack appear shielded as included in the picture
Other option is to build an amp practice space inside a faraday cage

Another thought would it help to put ferrite ring on that black cable coming from the input jacks? I do not think that would help as the 47uF caps did nothing

Here is why ChatGpt states I am still hearing RF
"RF coupling through the coupling cap (0.01 µF) into the grid node
– Even with a perfect tip-to-sleeve cap on your jack, a strong local station can sometimes bypass that by capacitively coupling into the 0.01 µF that sits between tip and grid. If RF is large enough, it can flow through that 0.01 µF coupling cap directly into the grid node (downstream of your 47 pF), so you still hear it."