ah, now I get it! It doesnt really sound too bad with the bias at 145 ohms, but it does sound much better without any. I guess I'll have to run it with it anyways though. Someone told me to run the plate at 150 and the grid at 90 to make it more linear. The datasheet says its design point maximum is 130, but the chart shows it run on all the way up to 300. So I take it 150 is ok? For my 12at7 preamp section, should I stick with the same plate voltage , just to keep the circuit simpler?
Also , I was wondering if there was a way to incorporate a pre-post gain setup, so I can dial in distortion. How would I do this? I was thinking of using one half of the 12at7 as the preamp, and then running the output of that (with a pot) into the input of the other half, and then from that to another pot and into the 50c5. Will this work out ok ?
Also , I was wondering if there was a way to incorporate a pre-post gain setup, so I can dial in distortion. How would I do this? I was thinking of using one half of the 12at7 as the preamp, and then running the output of that (with a pot) into the input of the other half, and then from that to another pot and into the 50c5. Will this work out ok ?
I did, butunless I missed something I couldn't really find anything close to what I'm looking for. I can find schematics for a 12axx preamp, but none for distortion that are simple
Thats why I was asking if its possable to use one half of the 12at7 for a preamp ( well, I know that part is true ) And then use the other half as another preamp, series connected with the other half. That way I can get an amped signal, and then run it into the other preamp causing distortion, then run it into the power amp tube. Basically so I can get distortion at lower volumes, you get the idea. Kinda like a plug in overdrive unit, only built in using both halves of the 12at7. I would think It could be done, I was really only asking if you its safe
What should my plate current be at 150v? Its a little hard to calculate it from this datasheet
I would also like to be able to swap between the 35c5 and the 50c5. I think the voltages will work , All I have to do is drop 50v to 35v on the heater.
Thats why I was asking if its possable to use one half of the 12at7 for a preamp ( well, I know that part is true
) And then use the other half as another preamp, series connected with the other half. That way I can get an amped signal, and then run it into the other preamp causing distortion, then run it into the power amp tube. Basically so I can get distortion at lower volumes, you get the idea. Kinda like a plug in overdrive unit, only built in using both halves of the 12at7. I would think It could be done, I was really only asking if you its safe What should my plate current be at 150v? Its a little hard to calculate it from this datasheet
I would also like to be able to swap between the 35c5 and the 50c5. I think the voltages will work , All I have to do is drop 50v to 35v on the heater.
Hi ThSpeakerDude88,
You can swap a 12AT7 for a 12AX7 for the purposes of your experiments. The parameters are a little different between those tubes but guitarists swap them around all the time. So build the 12AX7 circuit and play.
Whatever your cathode current is for 130V, reduce it a little. Measure the voltage across the tube from plate to cathode, multiply that by the plate current. That is your plate dissipation. It should be around 5.7~6 watts. The maximum plate dissipation is 7 watts.
The 35C5's maximum plate dissipation is 5.2 watts. You will have to increase the cathode resistance to swap to this tube. (decrease the plate current). This might be just over 4 watts.
-Chris
You can swap a 12AT7 for a 12AX7 for the purposes of your experiments. The parameters are a little different between those tubes but guitarists swap them around all the time. So build the 12AX7 circuit and play.
Whatever your cathode current is for 130V, reduce it a little. Measure the voltage across the tube from plate to cathode, multiply that by the plate current. That is your plate dissipation. It should be around 5.7~6 watts. The maximum plate dissipation is 7 watts.
The 35C5's maximum plate dissipation is 5.2 watts. You will have to increase the cathode resistance to swap to this tube. (decrease the plate current). This might be just over 4 watts.
-Chris
ok thanks. I will add in a resistor to switch also so I can drop the plate current for the 35c5. The reash I want to switch between tubes is because the 50c5 is cleaner and louder,distorts at higher volume and is harsher, and the 35c5 has awarmer breakup but at a lower volume ( from what I set up and played around with )
I got the 12AT7 up and running as a preamp, but it isn't very loud. I found schematic for one that used a 18k resistor between B+ and plate, and 33uf cap and 330ohm grid resistor/capacitor.
All I got with the 18k was a nasty power hum, so I increased it to around 81k and got it sort of clear, but theres a little bit of buzz and its not too loud, certainly not loud enough to push the power amp tube to distortion.
)I got the 12AT7 up and running as a preamp, but it isn't very loud. I found schematic for one that used a 18k resistor between B+ and plate, and 33uf cap and 330ohm grid resistor/capacitor.
All I got with the 18k was a nasty power hum, so I increased it to around 81k and got it sort of clear, but theres a little bit of buzz and its not too loud, certainly not loud enough to push the power amp tube to distortion.
Yes, treat them as separate tubes. The sections are not matched. The only consideration you need to give them is heater to cathode voltages if you use 1/2 as a voltage follower. Possibly capacitance between plates at high frequencies and impedance's. Otherwise they are each onto themselves.
-Chris
-Chris
well Ive been playing around with it for a while, so far I have it up and running! I have a pre/post gain setup so I can dial in distortion, and I'm running the 35c5/ 50c5 through my peavey blue mravel 8 inch woofer, it sounds GREat and is very loud for its power, considering I also have a trashy opt it sounds very good.
Infortunatly, I had the 12at7 connected to my secondary transformer. My secondary has a 20v output, and dual 12v and a center tap. I had it connected to 12v, but I accidentally shorted my cathode on the 50c5 , and with more current going into the tube from my bigger transformer, it drew more current from the secondary transformer and the voltage spiked on the 12v section and blew the heaters in the 12at7
I should have known better and ran it off of a regulated source...oh well. I think I will get a lot of 12ax7's and 12at7's off of ebay, as I still need the 12at7 in one of my radios.
Ok so now I have another question, Can I resistance couple either the 35/50c5 or the 42 ? I would like to resistance couple the 42, as I don't have an apropriate output transformer... unless I can add a resistor to equal the 7k ohm It needs, as my transformer is only 1.5k.
Infortunatly, I had the 12at7 connected to my secondary transformer. My secondary has a 20v output, and dual 12v and a center tap. I had it connected to 12v, but I accidentally shorted my cathode on the 50c5 , and with more current going into the tube from my bigger transformer, it drew more current from the secondary transformer and the voltage spiked on the 12v section and blew the heaters in the 12at7
I should have known better and ran it off of a regulated source...oh well. I think I will get a lot of 12ax7's and 12at7's off of ebay, as I still need the 12at7 in one of my radios.
Ok so now I have another question, Can I resistance couple either the 35/50c5 or the 42 ? I would like to resistance couple the 42, as I don't have an apropriate output transformer... unless I can add a resistor to equal the 7k ohm It needs, as my transformer is only 1.5k.
Hi ThSpeakerDude88,
If you resistance couple a speaker, your output power will be very small. I'm not going to try and figure it out. You need the output transformer to take the high voltage low current signal from the output tube and transform it to a lower voltage, higher current. This can drive your 8 or 4 ohm speaker.
If they could have done it this way, they would have. Keep your eyes peeled for maore garbage units.
-Chris
If you resistance couple a speaker, your output power will be very small. I'm not going to try and figure it out. You need the output transformer to take the high voltage low current signal from the output tube and transform it to a lower voltage, higher current. This can drive your 8 or 4 ohm speaker.
If they could have done it this way, they would have. Keep your eyes peeled for maore garbage units.
-Chris
alright, that makes sence, since there is low current on the plate and loudspeakers are high current devices.
I have a few old transformer cores..I think Im gonna end up winding my own for now untill I can afford some real ones. By the way, how do I measure a transformer's resistance? I try measuring the one from my old radio, but all I get is 1 ohm on the 8 ohm side (if that) and 200some on the primary side..
I have a few old transformer cores..I think Im gonna end up winding my own for now untill I can afford some real ones. By the way, how do I measure a transformer's resistance? I try measuring the one from my old radio, but all I get is 1 ohm on the 8 ohm side (if that) and 200some on the primary side..
Hi ThSpeakerDude88,
Okay, now you are into territory I only have a light understanding.
You can not measure DC resistance of the coil. You can measure the inductance. An AC signal is used for the. You can also measure the ratio by applying a known AC signal on the primary and measuring the voltage on the secondary. Normal test frequencies seem to be 1 KHz and 400 Hz. There is a formula to figure out what the impedance ratio is. I can't think of it right off hand.
There are members who are far more knowledgeable than I am. This might be a good new thread.
-Chris
Okay, now you are into territory I only have a light understanding.
You can not measure DC resistance of the coil. You can measure the inductance. An AC signal is used for the. You can also measure the ratio by applying a known AC signal on the primary and measuring the voltage on the secondary. Normal test frequencies seem to be 1 KHz and 400 Hz. There is a formula to figure out what the impedance ratio is. I can't think of it right off hand.
There are members who are far more knowledgeable than I am. This might be a good new thread.
-Chris
Alright I finally built a voltage doubler so I could run he 50c5's filiment at 50v (before all I had was a 32v switchmode)
It seems to work absolutly great! I even had it on for about 6 housr last night just using it for my computer's amp while playing halo with a friend. It got hot, but seemed to stay within reason.
I think my output transformer is too small because when you really try and run volume through it it saturates easily (mostly the high end) and you can hear music in the transformer...
Also, I still have a slight hum when the amp is running. Not enough to be annoying ( its real quiet) but enough to know the amp is on when your in the room. Its not a buzz, its a hum. What can I do to fix this?
I was also wondering what you think of a voltage um...how would I put it, pentupler? well anyways a voltage quadupler with one more on it to take the 24v transformer and step it up 5 times to around 150v. With my heaters tapped at the 64v section ( draeing 150ma for the 50c5 and (?) for the 12axx (havent equated that in yet) and the plates consuming a total of maybe 100ma ( to have some headroom) I actually measure about 63v on the heater of the 50c5 (ive since put a voltage dropping resistor) So I think it doubles a little more than 24v.
but anyways, I think it would make it a lot smaller and simpler for me ( I want it to be portable)
because I could do one of two things: 1) Buy a 24vac 1amp wall wart, or
2) mount a 24v 1amp transformer on the chassis.
I think I want to go with the first one so I can keep the size of the amp to a minumum ( IE altoids container, only a little larger because of the filter caps)
It seems to work absolutly great! I even had it on for about 6 housr last night just using it for my computer's amp while playing halo with a friend. It got hot, but seemed to stay within reason.
I think my output transformer is too small because when you really try and run volume through it it saturates easily (mostly the high end) and you can hear music in the transformer...
Also, I still have a slight hum when the amp is running. Not enough to be annoying ( its real quiet) but enough to know the amp is on when your in the room. Its not a buzz, its a hum. What can I do to fix this?
I was also wondering what you think of a voltage um...how would I put it, pentupler? well anyways a voltage quadupler with one more on it to take the 24v transformer and step it up 5 times to around 150v. With my heaters tapped at the 64v section ( draeing 150ma for the 50c5 and (?) for the 12axx (havent equated that in yet) and the plates consuming a total of maybe 100ma ( to have some headroom) I actually measure about 63v on the heater of the 50c5 (ive since put a voltage dropping resistor) So I think it doubles a little more than 24v.
but anyways, I think it would make it a lot smaller and simpler for me ( I want it to be portable)
because I could do one of two things: 1) Buy a 24vac 1amp wall wart, or
2) mount a 24v 1amp transformer on the chassis.
I think I want to go with the first one so I can keep the size of the amp to a minumum ( IE altoids container, only a little larger because of the filter caps)
Hi ThSpeakerDude88,
Voltage regulation will be very, very poor for your HT supply. I would be tempted to use an isolation transformer. You can get those cheap in the 50W range. A travel transformer may be had around 25W I think. Stick your heaters in series with a dropping resistor and you're off to the races. Your hum may go away too.
-Chris
Voltage regulation will be very, very poor for your HT supply. I would be tempted to use an isolation transformer. You can get those cheap in the 50W range. A travel transformer may be had around 25W I think. Stick your heaters in series with a dropping resistor and you're off to the races. Your hum may go away too.
-Chris
In a case like this, I'd prefer to use a high frequency DC/DC inverter. The more stages you add to a Walton-Cockroft, the higher the internal resistance, and the worse the regulation. You could build an inverter, run that off a 12Vdc wall wart (DC doesn't need to be real clean here) and power the inverter. That way, you can get all the DC you need, for heaters and plates, and much less hum since the filter capacitors become more effective as frequency foes up.
You could wind the HF xfmr easily from an old TV horzontal deflection xfmr core.
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