Hi guys,
Im relatively new to the whole tube world.
I am wanting to build a 813 pp amp and I was wondering if anyone can point me in the right direction.
I have spent hours looking for schematics online but i don't know what to go with.
If anyone here is experienced with 813 pp amps and is willing to share there knowledge I would be more then grateful to listen.
My power supply is 2200v its salvaged out of a transmitter that was running the 813's.
I don't want to change the tube or the voltage. In New Zealand its really hard to find these items so its more of a matter of making the most of what you have got.
Thanks for your time
Andrew
Im relatively new to the whole tube world.
I am wanting to build a 813 pp amp and I was wondering if anyone can point me in the right direction.
I have spent hours looking for schematics online but i don't know what to go with.
If anyone here is experienced with 813 pp amps and is willing to share there knowledge I would be more then grateful to listen.
My power supply is 2200v its salvaged out of a transmitter that was running the 813's.
I don't want to change the tube or the voltage. In New Zealand its really hard to find these items so its more of a matter of making the most of what you have got.
Thanks for your time
Andrew
If that is the case, please learn everything about HV safety before you even begin the project. 2.2kV is not for beginners - proceed with caution.
Thanks guys, I worked around 11kv and 33kv for 3 years. I do tend to urge on the side of caution. I have had a look at the champ 1000, correct me if im wrong, but isnt that a PP mono block, so 4 813's per channel? im wanting something stereo.
Thank you for the information so far though, i really appreciate your time
Thank you for the information so far though, i really appreciate your time
I would not recommend an 813 amp as a starter in the world of valve audio. Quite apart from the high voltages, which the OP says he is familiar with, there is also the risk of the output stage becoming a high power RF oscillator. RF can be more dangerous than high voltage.
That is just one example, do you have the original schematic from the salvaged transmitter or the specifications for the output transformer? It might be suitable to use another output tube with it as DF96 suggested.
Hi guys,
On the old drawings of the transmitter that i am salvaging the power supply out of, its noted that the transformer is 2200v up to 500mA pk.
The cap is a 68MFD@5000v, The bleeder on the circuit is 200k. He has a soft start incorporated into the pri circuit.
The transformer had been proven to run two 813's, I don't know if I would get 4 out of it, (two mono blocks). I will try and do some digging around that transformer to see what amperage it throws out. It came out of a old diathermy unit. I doubt they would of put a info plaque on it for a production built transformer specific to a unit.
How ever, in all this reading, I am convinced that a 2ch 813 PP is the way to go for what I'm wanting.
Jazbo8, What do you recommend as a build? The Champ1000 looks pretty straight forward.
DF96, How would you ensure the output stage wouldn't become a RF osc.
Fortunately for me, I do have a couple of friends helping me with the build. They all come from a transmitting back ground, except they are all up around the 500kW + AM transmitters. But unfortunately for me, none of them are experienced with audio amps.
So here's hoping you guys could help me out.
Thanks for the input so far.
On the old drawings of the transmitter that i am salvaging the power supply out of, its noted that the transformer is 2200v up to 500mA pk.
The cap is a 68MFD@5000v, The bleeder on the circuit is 200k. He has a soft start incorporated into the pri circuit.
The transformer had been proven to run two 813's, I don't know if I would get 4 out of it, (two mono blocks). I will try and do some digging around that transformer to see what amperage it throws out. It came out of a old diathermy unit. I doubt they would of put a info plaque on it for a production built transformer specific to a unit.
How ever, in all this reading, I am convinced that a 2ch 813 PP is the way to go for what I'm wanting.
Jazbo8, What do you recommend as a build? The Champ1000 looks pretty straight forward.
DF96, How would you ensure the output stage wouldn't become a RF osc.
Fortunately for me, I do have a couple of friends helping me with the build. They all come from a transmitting back ground, except they are all up around the 500kW + AM transmitters. But unfortunately for me, none of them are experienced with audio amps.
So here's hoping you guys could help me out.
Thanks for the input so far.
nightowlandy
Before going any further down this road you must consider the most important part of ANY tube amplifier. This is the audio output transformer (OPT). Tubes are inherently high impedance devices (thousands of ohms), and your speakers are low impedance, like 4 or 8 ohms.
A tube amp of this nature will require a large purpose built transformer for each channel. It must be rated for the entire audio frequency range (20 Hz to 20 KHz), or less if you are willing to compromise, the full power output of the chosen tubes, and the impedance transformation required by those tubes.
For a pair of 813's operating on 2200 volts this will be 350 to 380 watts and 18,000 to 20,000 ohms stepped down to 4 or 8 ohms.
That will be a very LARGE and EXPENSIVE transformer that will probably need to be custom made. These are not in anybody's catalog.
I had some 813's and a big power transformer out of a Harris radio transmitter, but abandoned this idea when I couldn't find a suitable set of transformers for less than the cost of a new car!
I sold the 813s to ham radio people, but kept the big transformer. Someday I will build something big, but I learned to look for OPT's first, then find tubes and power transformers that will work with them. It has taken about 6 years, but I have collected a set of transformers for a 500 WPC tube amp that will run on about 700 volts and needs a 1250 ohm OPT.
The OPT gets harder to make and more expensive as the impedance ratio goes up. This makes most big RF transmitting tubes almost a non starter for quality audio.
Note the guy with the 1000 watt guitar amp made his own transformers. As the number of tubes goes up, the impedance goes down since they are in parallel, and a guitar amp doesn't need the entire audio range, 80 Hz to 5 KHz is sufficient. That OPT is doable with proper skills. 20,000 ohms over 20Hz to 20000 Hz probably isn't.
Before going any further down this road you must consider the most important part of ANY tube amplifier. This is the audio output transformer (OPT). Tubes are inherently high impedance devices (thousands of ohms), and your speakers are low impedance, like 4 or 8 ohms.
A tube amp of this nature will require a large purpose built transformer for each channel. It must be rated for the entire audio frequency range (20 Hz to 20 KHz), or less if you are willing to compromise, the full power output of the chosen tubes, and the impedance transformation required by those tubes.
For a pair of 813's operating on 2200 volts this will be 350 to 380 watts and 18,000 to 20,000 ohms stepped down to 4 or 8 ohms.
That will be a very LARGE and EXPENSIVE transformer that will probably need to be custom made. These are not in anybody's catalog.
I had some 813's and a big power transformer out of a Harris radio transmitter, but abandoned this idea when I couldn't find a suitable set of transformers for less than the cost of a new car!
I sold the 813s to ham radio people, but kept the big transformer. Someday I will build something big, but I learned to look for OPT's first, then find tubes and power transformers that will work with them. It has taken about 6 years, but I have collected a set of transformers for a 500 WPC tube amp that will run on about 700 volts and needs a 1250 ohm OPT.
The OPT gets harder to make and more expensive as the impedance ratio goes up. This makes most big RF transmitting tubes almost a non starter for quality audio.
Note the guy with the 1000 watt guitar amp made his own transformers. As the number of tubes goes up, the impedance goes down since they are in parallel, and a guitar amp doesn't need the entire audio range, 80 Hz to 5 KHz is sufficient. That OPT is doable with proper skills. 20,000 ohms over 20Hz to 20000 Hz probably isn't.
Perhaps the best place to start is to look at the schematic of the transmitter, it might be possible to modify it for audio use. So could you please post the schematic so we can take a look? Also whatever happened to the OPT that the transmitter used, did it get scraped?
If the transmitter was for CW or SSB there was no audio frequency transformer, only RF impedance matching components. If it was actually a linear amplifier (likely), it would also contain only RF matching components.
If the transmitter was originally an AM transmitter it would have had one modulation transformer. There would have been an RF amp ( probably the 813's) and a separate audio amp using the 813's or another tube (often 811A's) and a modulation transformer, or choke. A modulation transformer for any service other than broadcasting is usually designed for about 300 Hz to 3 or 4 KHz, and matches a high impedance to another high impedance. Even an AM broadcast transmitter has a restricted frequency response. Often 100 Hz to 10KHz.
I see, does the 813 have to be operated with such high voltage for audio? Lowering the voltage might make finding an OPT easier...
It can run lower. The spec sheet lists it down to 1.5 kv in class ab. It runs a little over 250 watts with an 9.3 kilo ohm output transformer.
Nick
Nick
It depends on what you want to do with the 813s. Is this a bigwatt guitar amp to fill a stadium with ear splitting sound? Is this for music reproduction? PA service? AM plate modulator?
You want bigwatts, you need bigvolts. The A Number One problem with high voltage operation is that you'll necessarily be deep into Class AB operation, with the problem of X-over distortion. That wasn't a factor for an AM plate modulator, or PA where the premium is lotsawatts with high efficiency, not sonic performance. Look at the schemo of that plate modulator a couple of posts up: no NFB, IST phase splitting, it has a diode clipper in the signal path -- there is nothing about that design that makes for the kind of sonic performance you'd want for music reproduction. It doesn't matter if there's x-over, THD, and lots of pentode nastiness. Once the clipper kicks in, that will make more distortion than anything else.
Dropping the voltage reduces power, but also allows for better sonic performance, as you're closer to Class A, and the load resistance will be lower, making for an easier to design and build OPT.
It can and does work at lower voltages. I have run them as low as 600 volts, but it you are going that low, there are plenty of other tubes that will work better, like just about any TV sweep tube. You can also triode wire the 813 from anything below 750 volts, and people have pushed that to around 1000 volts.
The OP has the original power transformer and stated that he did not want to change the tube or the supply voltage.
Seeing your post makes me wonder - If the original supply was only for two 813's and he want's stereo would it work to feed the original HV power transformer with say a roughly 100:50VAC step down transformer and then build Pete Millett's circuit?
Hi guys, there is no OPT on the transmitter. it was for use at 10m.
Im scratching my head over this whole PSU and OPT issue.
I listen to a wide range of genre so Im thinking PP is more for me. I would like a decent power output, I enjoy my Al Steward, Pink Floyd and The Who LOUD.
Since coming to the tube scene the 813 has always stood out to me, I would like to use it, if its practicable.
KT88's seem to be very common, I want to build something different. Also I want tubes to be use where ever possible. e.g rectifiers rather then diodes etc.
I appreciate all your comments, Im open to all your feedback.
Cheers
Im scratching my head over this whole PSU and OPT issue.
I listen to a wide range of genre so Im thinking PP is more for me. I would like a decent power output, I enjoy my Al Steward, Pink Floyd and The Who LOUD.
Since coming to the tube scene the 813 has always stood out to me, I would like to use it, if its practicable.
KT88's seem to be very common, I want to build something different. Also I want tubes to be use where ever possible. e.g rectifiers rather then diodes etc.
I appreciate all your comments, Im open to all your feedback.
Cheers
Hi
Is the power supply complete or just the HT transformer? just that you mention wanting to go to tube rectification? 866 mercury rectifiers! silicon might be a better idea for your first project
Also, do you have the filament transformer? These beauties will draw 5 amps each but glow so nice 🙂
Cheers
Is the power supply complete or just the HT transformer? just that you mention wanting to go to tube rectification? 866 mercury rectifiers! silicon might be a better idea for your first project
Also, do you have the filament transformer? These beauties will draw 5 amps each but glow so nice 🙂
Cheers
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