Just picked up this Mid 30s Rickenbacher
- Thread starter Jewellworks
- Start date
Boreas
Doctor of Teleocity
AWESOME! I have a Rickenbacher lap steel from around WW2 perhaps.
Uncle Doug would love to get his hands on that amp to refurbish!!
Uncle Doug would love to get his hands on that amp to refurbish!!
Jewellworks
Tele-Holic
Pink? You mean violet?
Take those shades off there buddy.
Looks pink to me....
Jewellworks
Tele-Holic
Finally drew up an accurate schematic
Some of these antique resistors are still a mystery, and I wrote out the values read one way, and then the other (ie; the grid leak can either be 2.4k or 520k... Others too. I'm guessing 520k in this instance).
I'm also seeing a large imbalance between the plates of the 47s. 10k on 1 side, and 2, 430k resistors in series, for a total of 860k on the other side. Why 2?
I powered it up without tubes and got an HT of 390VAC w/no load. 3.1v on the filaments.
It also has a 3A fuse, which seems enormously high, but maybe not. I haven't really looked too closely at the data sheets for current draw.
I'm half-debating whether to keep it original, with all the same values, or make a few changes and possibly make it sound better. ie; change out the .1uf coupling caps for .01uf... Maybe add a bypass cap on the cathode of the preamp /PI? Maybe... Or change the input to a high impedance w/a 1M to ground? Or add screen resistors? Seems to me the screen will have a higher voltage than the plates.
But then again, this is a historical piece, and it is what it is... I shouldn't try an make it into a Fender, so probably not...
Where can I get a vintage style leather handle for this beast?
I'm nearly ready to start on this. Yeeeeeee
Some of these antique resistors are still a mystery, and I wrote out the values read one way, and then the other (ie; the grid leak can either be 2.4k or 520k... Others too. I'm guessing 520k in this instance).
I'm also seeing a large imbalance between the plates of the 47s. 10k on 1 side, and 2, 430k resistors in series, for a total of 860k on the other side. Why 2?
I powered it up without tubes and got an HT of 390VAC w/no load. 3.1v on the filaments.
It also has a 3A fuse, which seems enormously high, but maybe not. I haven't really looked too closely at the data sheets for current draw.
I'm half-debating whether to keep it original, with all the same values, or make a few changes and possibly make it sound better. ie; change out the .1uf coupling caps for .01uf... Maybe add a bypass cap on the cathode of the preamp /PI? Maybe... Or change the input to a high impedance w/a 1M to ground? Or add screen resistors? Seems to me the screen will have a higher voltage than the plates.
But then again, this is a historical piece, and it is what it is... I shouldn't try an make it into a Fender, so probably not...
Where can I get a vintage style leather handle for this beast?
I'm nearly ready to start on this. Yeeeeeee
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Lingwendil
TDPRI Member
Replace every single capacitor before you power it up! All of them are beyond their useful and safe life by now. Often recapping is good enough to let you fire it up and measure voltages. Resistors may or not be fine, depends on how this thing was used and stored.
NTC
Tele-Afflicted
- Joined
- Mar 17, 2003
- Posts
- 1,512
Not trying to be a smarty pants - you DID look at the schematic on the page printer2 linked, yes? Where you have 2.4k and a 130 ohm, they have 220k and 13k. These values seem reasonable. Also, that schematic has 47k plate resistors for the triodes. Some of these have probably been replaced over the years. Personally, I would try to keep the circuit as close to original as possible when replacing parts. At least as a start.
Directly heated tubes tend to have higher filament currents than we are typically used to. Look at the datasheets.
Directly heated tubes tend to have higher filament currents than we are typically used to. Look at the datasheets.
Jewellworks
Tele-Holic
Quick update:
After looking at the "antique" resistor code posted by @corliss1 , the resistor values started making a LOT more sense and much closer to the schematic on the link posted by @printer2 . In fact, they're so close, I'm considering leaving them in there.
Looking at other pictures of this amp on the web made it clear this was serviced at some point. They changed the power cord, and changed 1 resistor from 150k, to a 470k, then added another 470k in series, for a total of nearly 1M. That threw the balance between the triodes WAY off, ...and confused me. What were they thinking??
That said, the only other question mark is the flat resistor on the CT of the heaters. Since the 47 tubes are directly heated, they're also the cathodes, so I'm guessing its the bias resistor for the 47 tubes. Question is; is it correct? It says 742 on it, but it measures 223. -leave it? I'd sure like to find a characteristics curve so I can figure out the bias at 120 volts as opposed to 110... Same with the 57 tube and that 860 (750) cathode resistor
After looking at the "antique" resistor code posted by @corliss1 , the resistor values started making a LOT more sense and much closer to the schematic on the link posted by @printer2 . In fact, they're so close, I'm considering leaving them in there.
Looking at other pictures of this amp on the web made it clear this was serviced at some point. They changed the power cord, and changed 1 resistor from 150k, to a 470k, then added another 470k in series, for a total of nearly 1M. That threw the balance between the triodes WAY off, ...and confused me. What were they thinking??
That said, the only other question mark is the flat resistor on the CT of the heaters. Since the 47 tubes are directly heated, they're also the cathodes, so I'm guessing its the bias resistor for the 47 tubes. Question is; is it correct? It says 742 on it, but it measures 223. -leave it? I'd sure like to find a characteristics curve so I can figure out the bias at 120 volts as opposed to 110... Same with the 57 tube and that 860 (750) cathode resistor
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Sorry, fools rush in -- I've been trying to ID in the photos the 'flat resistor' you mention. Did someone decode this text on the schematic from @printer2 ?
FWIW, y'all will have sussed that the star / asterisk leads to this helpful suggestion: "see notes in manual."
FWIW, y'all will have sussed that the star / asterisk leads to this helpful suggestion: "see notes in manual."
OK, so what's the Rickenbacher vs Rickenbacker story? Doesn't seem to be acknowledged here:
www.rickenbacker.com
Early History of Rickenbacker
Stevo Bambino
TDPRI Member
On the same website that Printer2 linked to, there is another entry for Version 2 of the same amp. The schematic is very similar, uses 47 tubes, and shows a 200 ohm resistor for the center tap of the filament winding. 223 ohm is not that far off and from Jewellwoks photos it appears to be a wire wound resistor. In my experience, when a wire wound resistor goes bad, its goes open, i.e. it not longer conducts anything. I have never seen one drift. I am not saying they don't drift, just that I have never seen one.
Wyatt
Tele-Afflicted
- Joined
- Nov 3, 2004
- Posts
- 1,378
OK, so what's the Rickenbacher vs Rickenbacker story? Doesn't seem to be acknowledged here:
Early History of Rickenbacker
The company was founded as Ricknebacher and changed to Rickenbacker in 1946. Adolph Rickbacher was Swiss, and often anglicized his name to Rickenbacker more than once to avoid being perceived as German just after WWI and WII.
Good info. And yeah, not only is '742' too precise / arbitrary to be a value, but I’m thinking something around 200 or 220 ohms would be typical for an artificial CT.
Jewellworks
Tele-Holic
isaacteller
TDPRI Member
These 2 schematics might help.
Jewellworks
Tele-Holic
It's equally unhelpful because it only shows the heater voltage, not the resistor. In fact, it doesn't show a resistor at all. I suppose that info is revealed when you follow the star... "notes in manual". However, as noted earlier, the Model 2 is nearly identical except for the heater voltage, but it shows a 200ohm resistor on the CT.
Jewellworks
Tele-Holic
and just to keep everyone up to date, below is a 99% accurate schematic of what is in here. im still not convinced the HT has a center tap. i see a wire going to ground out of the PT, but not sure if it is the transformer plate ground, or the HT CT. these old cloth covered wires has VERY subdued colors after 86 years, but the ground wire in question is definitely NOT Red/Yel. its solid Black.
of course, some of these values dont exist anymore as standard resistors, so we need to use whatever is close enough...
and correct me if im wrong, but seeing as the 80 is a full wave rectifier, it doesnt need (or want) a CT on the HT. i know ive built solid state full wave diode rectifiers, and im not using a CT.
i removed the speaker last night, and it is in excellent condition.
at some point, this amp was dropped and the steel cabinet was warped and wobbly. i did some strategic banging on it, and its pretty damn square again and not wobbly anymore. gonna clean it up, get some of the grunge and dirt out of the crinkle paint, and then wax it to spiff it up a bit.
im about to order some Caps, (all 650v) and i hope to have them by next weekend and have this guy up and running again.
im also ordering some vintage style, cloth covered, 3 wire power cord wire, and a vintage style 3 prong plug to go with it. i also found a guy on ebay making arrowhead leather handles which would be perfect for this amp, but geez... he wants $60 after shipping...
i hope the tubes are good. i still need to invest in a tube tester. if theyre bad, they run about $20 each...
this old feller will be brand new again.
of course, some of these values dont exist anymore as standard resistors, so we need to use whatever is close enough...
and correct me if im wrong, but seeing as the 80 is a full wave rectifier, it doesnt need (or want) a CT on the HT. i know ive built solid state full wave diode rectifiers, and im not using a CT.
i removed the speaker last night, and it is in excellent condition.
at some point, this amp was dropped and the steel cabinet was warped and wobbly. i did some strategic banging on it, and its pretty damn square again and not wobbly anymore. gonna clean it up, get some of the grunge and dirt out of the crinkle paint, and then wax it to spiff it up a bit.
im about to order some Caps, (all 650v) and i hope to have them by next weekend and have this guy up and running again.
im also ordering some vintage style, cloth covered, 3 wire power cord wire, and a vintage style 3 prong plug to go with it. i also found a guy on ebay making arrowhead leather handles which would be perfect for this amp, but geez... he wants $60 after shipping...
i hope the tubes are good. i still need to invest in a tube tester. if theyre bad, they run about $20 each...
this old feller will be brand new again.
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Riff Ron
TDPRI Member
Those wax coupling caps will have to go as they are surely leaky by now. All electrolytic capacitors will have to be replaced. All screen resistors should be tested and replaced if needed. Finally check the power supply resistors and bias components. Also check tubes. Don’t fire it up without a current limiter light bulb.
Tube testers are, mostly, a joke. They test at voltages that are too low for you to know if a tube is good. In general, a tester can tell you if a tube is bad, but it can't tell if you if it's good. The best tube tester is the device you plan to use it in - aka, the amp.
