Motorola
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wa2ise
Super Member
Yes, cheaper, and if it's in a self contained box, like a phonograph cabinet, the shock hazard is brought down to a reasonable level. The user can't normally access this amp, as it's inside the record player cabinet, and the speakers are isolated via the output transformers.
Just don't touch the chassis while its on, and never under any circumstances connect this to something with a grounded power cord or other connection to ground (tv set, cable box, etc) and you'll be OK. I'd actually suggest building a small cabinet of some sort out of wood or another non-metal material if you want to make regular use of it. With a 35c5 output tube its not going to make a lot of power, maybe 5w per channel but it wouldn't be a bad low power amp.
Shouldn't be a selenium rectifier in this. The 35W5 is the rectifier tube for B+.
Shouldn't be a selenium rectifier in this. The 35W5 is the rectifier tube for B+.
electroking
a- v- karma member
5 WPC sounds optimistic
According to the RCA data, with a plate voltage of 110 volts, the 35C5
has a maximum power output of 1.5 W with 10% THD. Don't expect
thundering bass from such a small amp...
According to the RCA data, with a plate voltage of 110 volts, the 35C5
has a maximum power output of 1.5 W with 10% THD. Don't expect
thundering bass from such a small amp...
OK, I guess I was giving it a bit too much credit then 
Didn't have my tube manual on hand, that was just a guesstimate. Most of the AA5 type sets I've seen that tube in the output stage of had a 3-5 watt speaker. They do get rightly nasty sounding if you try and drive them too hard though.
Didn't have my tube manual on hand, that was just a guesstimate. Most of the AA5 type sets I've seen that tube in the output stage of had a 3-5 watt speaker. They do get rightly nasty sounding if you try and drive them too hard though.
Here's a thought I've been having, regarding the need for isolating the power on these old power-transformer-less chassis:
Find a transformer from a dead solid state receiver, dead subwoofer plate amp, etc... what you're looking for is something like 27-0-27 and 32-0-32 volt secondary... or, whatever you can wire up to get between 54 and 64 volts AC on the secondary. Those should be very common...
Then, use a VOLTAGE DOUBLER (two diodes and two caps- you can look at the schematic for the HK Award series integrated amps- A300, A500, etc- to get an idea of the wiring), to generate between 110 and 125v, DC (RMS). Feed this in, right into the AC cord of the unit. You might have to reverse the cord, to get it to work right... but, since most of these units were made to run AC or DC, this will usually work...
If the unit works with either polarity, find the orientation that puts the chassis at the LOWEST voltage (ie, common to the negative side of your power supply... this will make it "more like convention" from a service standpoint...
Of course, if you also have a record player hooked up to the same voltage, it will have to still be supplied from AC, usually. You may have to modify the wiring, accordingly.
I'm going to try this idea out on an old Magnavox table-top unit I have here... I think this might be a really good cheap-o idea, to both quiet the power supply (both the heaters and the B+ will have cleaner DC power), and to make the unit SAFE (ie, NOTHING directly connected to the 110V line cord on the chassis!)...
Regards,
Gordon.
Find a transformer from a dead solid state receiver, dead subwoofer plate amp, etc... what you're looking for is something like 27-0-27 and 32-0-32 volt secondary... or, whatever you can wire up to get between 54 and 64 volts AC on the secondary. Those should be very common...
Then, use a VOLTAGE DOUBLER (two diodes and two caps- you can look at the schematic for the HK Award series integrated amps- A300, A500, etc- to get an idea of the wiring), to generate between 110 and 125v, DC (RMS). Feed this in, right into the AC cord of the unit. You might have to reverse the cord, to get it to work right... but, since most of these units were made to run AC or DC, this will usually work...
If the unit works with either polarity, find the orientation that puts the chassis at the LOWEST voltage (ie, common to the negative side of your power supply... this will make it "more like convention" from a service standpoint...
Of course, if you also have a record player hooked up to the same voltage, it will have to still be supplied from AC, usually. You may have to modify the wiring, accordingly.
I'm going to try this idea out on an old Magnavox table-top unit I have here... I think this might be a really good cheap-o idea, to both quiet the power supply (both the heaters and the B+ will have cleaner DC power), and to make the unit SAFE (ie, NOTHING directly connected to the 110V line cord on the chassis!)...
Regards,
Gordon.
