I'm looking to replace the Tube in the schematic of an AP-951 refered to as UX-874 with a UP-591. I can't find any info on the UP-591, does anyone know where I can fine one or an equivalent? The UP-591 i think has a 1500 ohm resistance. Any info would be appriciated.
Thx

Pete there is two of these tubes the 874 is a ballast tube still quite common on ebay..it screws in ..It is nothing more that a string of resistance in a large glass envelope (vacume sealed)... Also the 951 is also not a tube it is a resistor sealed in pocelin.....I have one that was bad ..I took (broke) top off and picked out the plaster the resistor is sealed in. I put a new one in and sealed off with cement and cemented top back on..All it is is a resostor sealed in porcelin and put into a 4 prong tube base.. Only two pins are used electronically..You could mount resistor underneath chassis but make sure it has room to stay cool cause it will run hot.

Pete I am sorry I made a mistake... I was refering to wrong tube when u said 874 tube I was thinking of the 876 that is a ballast for this supply... THE 874 AND THE UP951 are used in your power supply and are switched depending on what radio/speaker you are using with it... The 874 tube is ONLY used when you are NOT using the RCA 104 speaker with the power supply...When you ARE using the power supply with the 104 RCA speaker you are to use the 951 resistor in place of the 874.

Thanks that helps alot. So to make sure I'm understanding, if I use the RCA model 100 speaker I should be OK using the UX-874 rigth?

Pete

If you are using the RCA 104 speaker you should use the resitor unit 951

sorry for my confusion. I just want to make sure - I have the model 100 speaker not the 104, are they the same? Do I need the UP-591 with a Model 100 seaker? If I need a UP-591 do you know where I can get one? There are none on Ebay, it may be called something else, but when I search under UP-591 nothing comes up.
Thx

I have all the original RCA "radiola" manuals (models 28 and others) that use this and various other power supplies...an i believe you only need to use the up951 when ussing the RCA 104 speaker... GOOD LUCK with trying to find a up951 resistor unit.. I had searched for months and had to buy whol big kick ass power supply from a raio like yours just to get the resistor unit.. I have one extra but am keeping...The porcelin unit is nothing more that a large pocelin resistor..I was able to scape out inside and stuff a new resistor inside of porcelin tube...I used a 2 watt 1500 ohm resistor... If you have a old 4 prong tube base you could make this... Just use a 2 watt 1500 ohm resistor ..solder leads to correct pins and use a stiff portlen cement to copy original...Ad some brown pigment and origianl was brown...

George - you have been VERY helpful. I glad to find someone that can help me with completing the vintage system. The unit has a RCA model 28 radio, the question I still have is can I use the UV-876 in conjuction with the Model 100 speaker & Mod 28 radio?

Thx
Again

::OOPPS one thing we need to cover...Has your Radiola 28 been converted to AC operation if it has it will have a pack of condensers mounted where the batteries should be..If it has this "pack" RCA called it "AC package for radiola 28" "MODEL UP72" it came with a restistance strip you would put where battery terminals hook up to back of chassis..two new reostats, up951 resistor, and the pack ..This may of been done at factory or by someone..If not converted and your model 28 is still battery operated then in the main power supply you are going to use the 874 tube along with the 100, 100A, or uz132 speakers. If your model 28 has not been converted the reostats will be "touchy" or full loudness will be reached befor you get to the 1/2 way mark.

would you mind sending me you email address? That way I can take some pics for you to examine. I cant get to it tonight but will be able to get info tomorrow. My Email is petepaciorek@aol.com.
Pete