[via-venti]

Hi newbie here, I have bought one of these amps (mk1) as not working and am now trying to fix it.I am in the UK with 230v mains and the seller believed it was a 230v amp although never had it working, I have my doubts and before I go to the effort of getting a variac involved I wonder does anyone know the DC resistance of the primary winding of a 115v amp opposed to a 230v one.There are only two wires out of the primary so it's not got two windings as you would expect/hope.

[FullRangeMan]

Hi newbie here, I have bought one of these amps (mk1) as not working and am now trying to fix it.I am in the UK with 230v mains and the seller believed it was a 230v amp although never had it working, I have my doubts and before I go to the effort of getting a variac involved I wonder does anyone know the DC resistance of the primary winding of a 115v amp opposed to a 230v one.There are only two wires out of the primary so it's not got two windings as you would expect/hope.

Welcome to AC 
There is any indication back in the amp?

You could disconnect the secondary output from the amp, connect the transformer to the mains wall and measure the values ​​that the transformer is releasing.

[via-venti]

Got a variac and disconnected the secondaries as suggested and yes it is a 115v transformer. At least it isn't faulty as it was blowing fuses when tried at 230v.I'm of a mind to refurb the amp and get myself a stepdown transformer. I will replace all the electrolytics ,with that in mind as installed is 880uf X4 which I intend to replace with !000uf's .I understand this is the value used in the mk2 version, my other query is regarding the improvement gained in putting in chokes in the power supply .Anyone have a circuit of this giving the choke values?
regards

[FullRangeMan]

Got a variac and disconnected the secondaries as suggested and yes it is a 115v transformer. At least it isn't faulty as it was blowing fuses when tried at 230v.I'm of a mind to refurb the amp and get myself a stepdown transformer. I will replace all the electrolytics ,with that in mind as installed is 880uf X4 which I intend to replace with !000uf's .I understand this is the value used in the mk2 version, my other query is regarding the improvement gained in putting in chokes in the power supply .Anyone have a circuit of this giving the choke values?
regards

You can send this Trafo to rewind the primary to 230V or order a new transformer in a manufacturer with EI 0.3mm M6 lamination or better.

[opnly bafld]

Have you tried contacting RAM Tubes?

https://www.ramtubes.com/contact

[ArthurDent]

Greetings & Welcome to AC   

[richidoo]

Roger Modjeski hand wound his trannies, so they didn't have "adjustable" primary voltage via series OR parallel connections like commercial trannies do. He was a master winder, so you don't want to change/repair/replace it. The transformers are big part of what make those amps great. Use a step down to feed it 115.  In my experience tube amps sound better when fed by an external magnetic reservoir, like isolation/stepdown/balanced transformer.

I doubt you're going to surpass his design with random mods. Make it healthy and have a listen first. I think you'll be very happy. Friend's stock RM9 sounded better than my Manley Snapper monoblocks.

[mick wolfe]

Roger Modjeski hand wound his trannies, so they didn't have "adjustable" primary voltage via series OR parallel connections like commercial trannies do. He was a master winder, so you don't want to change/repair/replace it. The transformers are big part of what make those amps great. Use a step down to feed it 115.  In my experience tube amps sound better when fed by an external magnetic reservoir, like isolation/stepdown/balanced transformer.

I doubt you're going to surpass his design with random mods. Make it healthy and have a listen first. I think you'll be very happy. Friend's stock RM9 sounded better than my Manley Snapper monoblocks.

 

[via-venti]

Thanks for all the replies. I was thinking that a large step down transformer would act to smooth out any high frequency noise from the mains.Luckily construction sites here use 110v for hand tools so 110v transformers are readily available,and as my supply sits at 240v it should give me 115v nicely.As for random mods I thought the main circuit differences in the mk2 were increasing the power supply capacitors to 1000uf and also fitting chokes in the high voltage lines. I am wondering as i am writing if the ferrite sleeves in the mk2 description are the chokes being referred to?My mk1 has no ferrites.

[richidoo]

as my supply sits at 240v it should give me 115v nicely.

I have 123V mains and the RM9 performed great. I believe it is mk1.

As for random mods I thought the main circuit differences in the mk2 were increasing the power supply capacitors to 1000uf and also fitting chokes in the high voltage lines. I am wondering as i am writing if the ferrite sleeves in the mk2 description are the chokes being referred to?My mk1 has no ferrites.

Upgrading from mk1 to mk2 is not random. Wise move if you can find the upgrade details.

The terms are kinda interchangeable depending on the application, but "ferrite sleeve" or "ferrite bead" implies a high frequency filter on mains before the transformer; while "choke" implies a larger, wound inductor after rectification for ripple smoothing along with those 1000uF caps.


EDIT: My friend with the RM9 confirmed that his was originally mk1, but he sent it to Roger for conversion to mk2. He doesn't remember the details of the mk2 conversion but said it increased power output to 125wpc. So it was more than just PS filtering.

[richidoo]

Some details about the mk2 upgrades from Dick Olsher review 1994:
https://www.stereophile.com/content/music-reference-rm-9-power-amplifier-rm-9-mkii

[via-venti]

Have ordered up all electrolytics and have sent an email to ramtubes to see if I can get details on the chokes.Thanks.