"now i get a voltage of -37 to the grid which is good"
With 300 volts at the plate it isn't.
This is what you have to do:
1. Remove the fixed bias circuit, ground both 470k resistors.
2. Solder a 1k (2W) resistor to each cathode (pin 3). Measure the voltage at the cathode and also measure the plate voltage.
3. Report back with results.
With 300 volts at the plate it isn't.
This is what you have to do:
1. Remove the fixed bias circuit, ground both 470k resistors.
2. Solder a 1k (2W) resistor to each cathode (pin 3). Measure the voltage at the cathode and also measure the plate voltage.
3. Report back with results.
Hmm, I don't quite understand. The voltage doubler should provide about 320V, as measured. This is taken directly from the site with the schematic:
"Resistor R1 and capacitor C3 provide additional "smoothing" or "filtering" to reduce the amount of ripple on the DC supply. This is needed to reduce the amplifier's hum level to an acceptable level. A side effect is that there is some voltage loss (drop) across resistor R1, due to the current flowing through it. The net effect of this loss plus transformer losses is that the final voltage appearing at the output of the B power supply is approximately 215 volts during normal operation."
100V is a lot to drop. I would have expected to drop maybe 10-20V under load? Unfortunately, I believe that the original designer (Fred Nachbaur) has passed away(?). Did you, by chance measure the plate voltage when you had the tube in?
Sorry, my experience is limited, and I am stumped... Maybe cathode bias as suggested above is a good place to start...
"Resistor R1 and capacitor C3 provide additional "smoothing" or "filtering" to reduce the amount of ripple on the DC supply. This is needed to reduce the amplifier's hum level to an acceptable level. A side effect is that there is some voltage loss (drop) across resistor R1, due to the current flowing through it. The net effect of this loss plus transformer losses is that the final voltage appearing at the output of the B power supply is approximately 215 volts during normal operation."
100V is a lot to drop. I would have expected to drop maybe 10-20V under load? Unfortunately, I believe that the original designer (Fred Nachbaur) has passed away(?). Did you, by chance measure the plate voltage when you had the tube in?
Sorry, my experience is limited, and I am stumped... Maybe cathode bias as suggested above is a good place to start...
Yeah, I don't understand it either. He was a good designer, maybe he had power supply sag due to small transformers. Strange.
im going to have to order some of those resistors maybe ill get some in my variety pack.
when i plug in the unit it hums loudly from the speaker and then starts popping so i have to unplug it.
can i plug it in briefly without a load on the output transformer just to measure voltages. or i probably wont get a realistic reading then anyways. i have to get some 8 ohm resistors. how many watts in value should they be, 5 watts or so? how much current runs to the speaker you think.
the output transformer has a number of leads for different loads as shown in the attachment, so i hook ground to the black wire from the speaker and the common ground and the other wire for a 4 ohm speaker would be the orange one i would assume. is this correct?
again. thank you very much for the replies.
and i ordered extra tubes so if this one works then i can build another and have two mono blocks or i can build the PP design from the same website
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Don't keep trying, 37 volts is OK for a B+ 220 volts not for 300 volts. You'll just torture the tubes a little more. You will probably need another resistor for the PS, 100 Ohms is too low. See, you have to burn some volts, the change to cathode bias burns 35 but is not enough.
EDIT: 10K is too high for that tube. I would use the yellow or the green. Black to ground. 8 Ohms resistor should be at least 5 Watts for this amp.
The 1K resistors need to be 5 Watts, my mistake. Yo could also parallel two 2k(2 watts) resistors.
EDIT: 10K is too high for that tube. I would use the yellow or the green. Black to ground. 8 Ohms resistor should be at least 5 Watts for this amp.
The 1K resistors need to be 5 Watts, my mistake. Yo could also parallel two 2k(2 watts) resistors.
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I have been reading the 13em7 data sheet and I was impressed, nice curves! It reminds me the 2A3. The amp will probably sound very good. I also have changed my mind about the cathode resistor, better to stay on the safe side: get two 1.5k (5W) resistors. You will also need 2 100uf 100V caps to bypass the resistors. Too bad you can't buy all this in your area, you may need other resistors as well.
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i appreciate your optimism about the amp sounding good when it is working. i guess the output transformer is not for hifi since its frequency range is limited.
other people have built this circuit without tweaking it. i guess the voltage is supposes to drop when the thing is operating.
i have to go over the thing again to find out why it makes such horrible noises when i turn it on.
the slope of the load line is determined by the output impedance? ... the secondary wires?
thanks!
yeah!!
it's working!!
just one more problem, the volume control. when i turn it the output gets noisey but the volume isnt affected. i have the right lug to ground and the center and left one between the input jack and the grid of the preamp. hmm.
ill have to take a closer look 
all the voltages are as they are stated in the schematic. the plate voltage is about 220v and the grid is 35v.
when i remove the input the thing humms very loudly, a ground problem?
thanks for all your support during this emotionaly trying period of my life
it's working!!
just one more problem, the volume control. when i turn it the output gets noisey but the volume isnt affected. i have the right lug to ground and the center and left one between the input jack and the grid of the preamp. hmm.
ill have to take a closer look all the voltages are as they are stated in the schematic. the plate voltage is about 220v and the grid is 35v.
when i remove the input the thing humms very loudly, a ground problem?
thanks for all your support during this emotionaly trying period of my life
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got that volume control sorted out too! now it works 100% it has a nice tube sound. thanks for the help!
im playing an mp3 player through it, and it obviously isnt very loud so i suspect that if i plug a guitar into it that it will be even quieter. on the website he gives sound samples with a guitar i was kind of hoping to use this as a guitar amp with a travel guitar.
it sure sounds nice!
im playing an mp3 player through it, and it obviously isnt very loud so i suspect that if i plug a guitar into it that it will be even quieter. on the website he gives sound samples with a guitar i was kind of hoping to use this as a guitar amp with a travel guitar.
it sure sounds nice!
one problem was a "Feedthrough" capacitor of which i was ignorant so i replaced that. then the other problem was the input jack which was a whacky job - i dunno. i kinda arbitrarily took it out and used another and it works.
now i need some high efficiency speakers, another set of transformers for stereo sound to build another one.
if i play a guitar through this thing will it sound a lot more quiet than the mp3 player? this little amp only puts out 1 watt!
do you know of any high efficiency books shelf speakers for a good price?
now i know what voltage multiplier is and how to build one. this is a cool hobby
but it sounds really nice, very full and round and very little noise
Yes, hifi. Regulated power supply, two-stage diff amp driver with MOSFEt source followers. Bit off more than I could chew. Tubelab's diff amp driver works perfectly. The power supply had me stumped for a while. Had to teach myself some basic solid state concepts, so now that is fixed after blowing it up a few times. Now getting some noise (grounding issue I think) and some oscillation that I think is due to input and output being right next to each other. Have a licence renewal (every 3 months, arg!!!) tmorrow morning, then 4 weeks off to watch Tour de France and fix amp!
Cheers,
Chris
Cheers,
Chris
I don't buy that, lol. Those fixes won't change the B+ from 320v to 220v. I'm guessing the cathode wasn't grounded. Anyway, glad it's finally working. Now you need a guitar preamp or a pedal, and a 100dB/m speaker. Hey, this is a small world: there's a tube guitar pre at the same place you found that schematic. Now wait, another nightmare coming on- you'd better buy a cheap pedal.
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