: I would like to know where I might find the values for
: RCA resistors. Especially the ones used in the Radiola 17
: and Radiola 18. I have Riders #1 manual and RCA service manual
: and neither one has the values.
: Thanks
: Bud Geuvens
Grid leak for 27 detector should be 2-3 megohm..I failed to record the 2 detector plate resistors mounted on the bypass condensor box.,,, but you should see about 45 volts on the plate of the 27...
I wouldnt think you would have troble with these..
You can always just power up and check lugs 7 and 8 to lug 9 (ground) and check for 145 volts for your main supply and 165 volts to the 71a plate..
These will show high with no load, so if it reads somewhat higher than that (w/o load), most likely it's ok.
Those wirewounds wont lose value much like a carbon resistor.. If they are not open you shouldnt have to worry about replacements..
The writeup here at Na suggests they may have become overheated in the past due to location where there is little air circulation. Mine had no problems with the power supply.. Most of the problems you will find with improper operation will be found at the volume control or around the first rf amplifer tubes (antenna and input need some resistance to ground to operate, you may have to play with this some) provided none of your transformers are not open..
You may also try tweaking the small compression cap located in a hole at the bottom of the tuning gang tub.
Those old 18's are built like tanks.. measure out your voltages from the lugs per the manual and check your transformers...Then let'er rip..
No need to be concerned with exact values of those resistors if your voltages are in the general area..
I cant imagine one in worse condition than mine when i found it, but today it works great, tunes good with very little hum.. About the only thing i did really beside upgrading to better condition tubes was replace the vol control and leak off the antenna input until it stabilized and howl and squeal was eliminated throughout the vol range..
Nothing quite as pretty as an 18 with the top open glowing in a darkened room..
Good luck, keep us updated on your progress..
davep
: : I would like to know where I might find the values for
: : RCA resistors. Especially the ones used in the Radiola 17
: : and Radiola 18. I have Riders #1 manual and RCA service manual
: : and neither one has the values.
: : Thanks
: : Bud Geuvens
The Radiola 17, 18 & 33 have several design problems, one being the volume control. The volume is controlled only in the antenna circuit while the radios isn't shielded. Strong stations will come through without an antenna. To prevent this problem the coil area needs to be shielded. You can install a metal shield under two mounting screws of the chassis. I use copper clad PC board but aluminum will work.
This shielding will also help to prevent squeal. Manufacturers using metal cabinets didn't have these problems. Even the Radiola 33 which has metal for the front, sides and top has the problem.. The entire bottom of the radio is wood and needs a shield.
The RCA antenna volume control is linear. If it's operating smoothly and original, white ceramic, I wouldn't change it. Many have been replaced but this won't make a difference in signal control.
Another problem with these Radiolas is the power supply filtering. If a modern high quality speaker is used you will have excessive hum. The radio will be ok with an original RCA 100A speaker as it doesn't reproduce the low frequencies very well.
The power supply uses two chokes in a choke input filter circuit. They are both mounted in the same can. A choke input filter has a lot of ripple across it and this ripple is transferred to the second choke. To prevent this another filter capacitor is needed going into the first choke. This in turn will increase the B+ voltage. To reduce B+ a 1K @ 10 watt resistor needs to be added between the 80 tube and first filter choke.
Norm
: Thanks all for the info. Dave,I seem to be having problems also in the volume control area. I have measured all the voltages and to my suprise, they all checked in spec. When I turn the the radiola 18 on , I have very little control with volume. The radio comes on with somewhat medium volume even with the knob turned all the way to the left. If I turn it up, the volume stays the same until I get almost all the way and then it changes tone and starts to squeal. I checked the resistance and it does show smooth resistance all the way around with no open readings. How did you fix the problem? I see that it take a 2k pot but I am not sure which kind linear or audio? Any hints will be of great help. Thanks again. Bud Geuvens
mine had an open to ground besides some corrosion, so i went ahead and replaced it..
it worked fine although some overloading at the loud end.. a shorter antenna wire solved the problem in my case...
You might also switch around your 26's using the weaker tubes first and stronger ones as the sig progress's down the sig chain after you get your control right... This helped mine get mine under control and doesnt work as well unless the 26's are in a certain order..
Main thing is check your control ground and or/ sub a new control in place temporarly to make sure the wiper or corrosion isnt the problem before you remove the original..
Thanks for the info, norm.. i didnt know about the lack of shielding may contribute to the overloading..!
I'm using a 1938 RCA permanant magnet with an output trans mounted on the speaker and it works great and plenty of high freq (almost too much when loud, nearly hurts the ears!)..
Also as norm mentioned if youre using a 100a, you might want to check the rod inside and make sure it's free and not hung up against the blocks or coils..
: Thanks all for the info. Dave,I seem to be having problems also in the volume control area. I have measured all the voltages and to my suprise, they all checked in spec. When I turn the the radiola 18 on , I have very little control with volume. The radio comes on with somewhat medium volume even with the knob turned all the way to the left. If I turn it up, the volume stays the same until I get almost all the way and then it changes tone and starts to squeal. I checked the resistance and it does show smooth resistance all the way around with no open readings. How did you fix the problem? I see that it take a 2k pot but I am not sure which kind linear or audio? Any hints will be of great help. Thanks again. Bud Geuvens
: besides the things norm mentioned, check the control arm on that vol pot and make sure it's not loose, bent or corroded and/or it's grounded on the other end..all sounds like it's not passing rf if it's not increasing vol, and like norm mentioned it's getting through elsewhere..
: mine had an open to ground besides some corrosion, so i went ahead and replaced it..
: it worked fine although some overloading at the loud end.. a shorter antenna wire solved the problem in my case...
: You might also switch around your 26's using the weaker tubes first and stronger ones as the sig progress's down the sig chain after you get your control right... This helped mine get mine under control and doesnt work as well unless the 26's are in a certain order..
: Main thing is check your control ground and or/ sub a new control in place temporarly to make sure the wiper or corrosion isnt the problem before you remove the original..
: Thanks for the info, norm.. i didnt know about the lack of shielding may contribute to the overloading..!
: I'm using a 1938 RCA permanant magnet with an output trans mounted on the speaker and it works great and plenty of high freq (almost too much when loud, nearly hurts the ears!)..
: Also as norm mentioned if youre using a 100a, you might want to check the rod inside and make sure it's free and not hung up against the blocks or coils..
: : Thanks all for the info. Dave,I seem to be having problems also in the volume control area. I have measured all the voltages and to my suprise, they all checked in spec. When I turn the the radiola 18 on , I have very little control with volume. The radio comes on with somewhat medium volume even with the knob turned all the way to the left. If I turn it up, the volume stays the same until I get almost all the way and then it changes tone and starts to squeal. I checked the resistance and it does show smooth resistance all the way around with no open readings. How did you fix the problem? I see that it take a 2k pot but I am not sure which kind linear or audio? Any hints will be of great help. Thanks again. Bud Geuvens
As Dave mentioned, some of us have written in the values on schematics. The resistor divider on the Radiola 17, from left to right: 410, 3750, 2140, 205 and 1690 ohms. Knowing this might also be some help with Radiola 18.
Norm
: I would like to know where I might find the values for
: RCA resistors. Especially the ones used in the Radiola 17
: and Radiola 18. I have Riders #1 manual and RCA service manual
: and neither one has the values.
: Thanks
: Bud Geuvens