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I have experimented with the 833A in a SET amp design. From my experience I can state that the OPT will be the most critical component in an amplifier like this. The OPT is the most important component in any tube amp, especially a SET. I built a prototype amp using an 833A, and paid a well known transformer maker to make me a prototype OPT for about 50 watts of power and 5K ohm impedance. The transformer weighs about 15 pounds, and had no problem cranking out the bass, but had far too much HF roll off. Conversations with other OPT designers led me to believe that a full range OPT in this power level would be difficult and expensive. The project was abandoned for lack of a suitable OPT.
I found a Web page to show big SET amps by DIY as follows.
These amps are conservative usage compared with the plate
dissipation.
The tube names between Japanese and America's are as follows;
7T40=1000T
5T30=450TL
http://www5b.biglobe.ne.jp/~tritium/7t40amp.htm (sorry Japanese only)
These amps are conservative usage compared with the plate
dissipation.
The tube names between Japanese and America's are as follows;
7T40=1000T
5T30=450TL
http://www5b.biglobe.ne.jp/~tritium/7t40amp.htm (sorry Japanese only)
833 is pretty much different from 304Tl btw I second George Tubelab on OPT, I need to add that you really want to take care of the filaments heating as it can make a huge difference as well. I got quite a decent results using a special OPT made my Mike Lafevre of Magnequest, FS-100-PF,
20Hz:-1.75dB
20kHz:-0.8dB
Noise (shorted input):1.45mVrms@50Hz
details here
bitc*s brew
that amp was way too hot for a living room and a daily use
gianluca
20Hz:-1.75dB
20kHz:-0.8dB
Noise (shorted input):1.45mVrms@50Hz
details here
bitc*s brew
that amp was way too hot for a living room and a daily use
gianluca
Michael,
I was planning on using an EML 20b, but the 30 might be a better choice?
here's the web page with the data:
EML-20A-20B-30A Datasheet. By Emission Labs.
The amp wil (almost) parallel the 437a / 320B jobbie you helped me with last year..Direct coupled with stacked supplies with a choke loaded driver. I plan to use MQ's "Dowdy" plate choke here. It's around 125hy, 40ma. with about 416dcr.
I'll shoot you the chicken scratch schmo (not as polished as the old one) Still working out the -bias schemes on the driver and the 304TL. Open to suggestions here.. Hope your holidays have been good!
Jeff
I was planning on using an EML 20b, but the 30 might be a better choice?
here's the web page with the data:
EML-20A-20B-30A Datasheet. By Emission Labs.
The amp wil (almost) parallel the 437a / 320B jobbie you helped me with last year..Direct coupled with stacked supplies with a choke loaded driver. I plan to use MQ's "Dowdy" plate choke here. It's around 125hy, 40ma. with about 416dcr.
I'll shoot you the chicken scratch schmo (not as polished as the old one) Still working out the -bias schemes on the driver and the 304TL. Open to suggestions here.. Hope your holidays have been good!
Jeff
Front end gain you need depends on your source voltage and load line of the output tube, plus/minus any drive margin you choose.
I would stick to lower Rp tubes for choke loading, which may exclude the 30A and leave you a front end gain of 20. The example 304tl load line above would need about 8V P-P input signal (2.83VRMS) to develop full power using a front end gain of 20.
Michael
Ok I was surfing and saw an amp made up with a 450tl tube; MIGHTY impressive looking, but cooler heads prevailing I'm also thinking 304tl. Something about 6kv puts me off. So my question to you all is, have anyone one actually built and finished a 304 amp and if so does it sound as good as you were hoping? Yes I know Alumatech has them but $85k is just a BIT dear!! Thanks ron parola
Definitely a transformer puzzle. I had some luck prototyping an 833A SET back in the mid-late 90's by using two Sowter 10k OPTs in parallel. I think he intended these for 211 service at a 20w rating. I don't recall the result rolling off too bad.
Gluca said:
Tell me about it! That is why I never tried to build more than a prototype of one channel. There was no way that was going into my living room. Not to mention the size and weight. I am afraid these extra big transmitter tube amps are for younger people with no wives, kids or pets!
That is why parafeed is quite a logical decision to make with such a tube. As Reinoutdv has done.
http://www.diyaudio.com/forums/tubes-valves/24424-where-833-amps.html
You had best make 0% errors working around these sorts of voltages, especially backed with the current you boys are talking about. You will get very DEAD FAST if you make one single mistake!
Which is why these "open" construction units with exposed plate caps and the like are an extremely BAD idea.
Nothing wrong with being able to see the tube - but it should never ever be open and exposed so that it can be physically touched while the power is on.
There are a number of attractive means of making the tube visible nicely without the exposure to DEADLY DANGEROUS VOLTAGES. Use them.
Remember you only get one time to make the mistake - then ur dead.
_-_-bear
Which is why these "open" construction units with exposed plate caps and the like are an extremely BAD idea.
Nothing wrong with being able to see the tube - but it should never ever be open and exposed so that it can be physically touched while the power is on.
There are a number of attractive means of making the tube visible nicely without the exposure to DEADLY DANGEROUS VOLTAGES. Use them.
Remember you only get one time to make the mistake - then ur dead.
_-_-bear
Here's my amp schematic still under development. I just decided to go the Parafeed route on the output. I have some of the iron on order and most of the other parts on hand. Plate choke on the EML20B is a MQ "Dowdy", the plate choke on the 304TL is from Electra-Print. Next couple of days I'll be ordering a Tribute Amorphous "C" core output transformer. Plus a few pairs of rubber gloves and boots!
Jeff Davison
Jeff Davison
Attachments
Thanks! A gentle or not-so-gentle reminder can't hurt. Here's a thought:
How close would you stand to a 6 foot diameter saw blade spinning at 5,000 RPM? This can kill you about as quickly and deserves the same respect.
Michael
PS IMO insulating your body is insufficient protection. Attitude and procedures are very important, and the general safety of your rig e.g. things bolted down, physical barriers, uncluttered work area. Stand back any time power is applied, and be wary of accidentally energized test equipment. Accidents happen due to the things you don't think about. Think things through to eliminate the chance of contact with the HV.
Even 300V DC is pretty dangerous, but damage potential goes up as the square of the voltage. 1500V will supply 25 times as much energy as 300V.
Read the HV Safety sticky thread
Could be the supply going into overcurrent. A cold filament would appear as almost a dead short before its warmed up.
The heater requirements for the 304TL are quite "rigorous" 5 volts but at 25 amps... yep twenty five. In a single end configuration, AC , even with all the "bells and whistles"..ie, hum pot, twisted pair leads etc.. will have a fair ammount of hum. DC is much better, but a normal DC supply (as used for the lower tube) can not be built to regulate all that current. Also finding chokes at 25A is fairly difficult in appropriate (non-microwave) frequencies / Henries, that aren't the size of a small automobile.
Each tube has to have it's own heater supply, they can not be shared as this is a two stage using DHT, where the cathode is also the heater/filament.
AC is said to sound good as a heater voltage supply( but can have a hum problem if not properly implemented), and series regulated DC less so, DC shunt regulation supposedly sounds better than series, and a Voltage controlled Current supply supposedly is the best DC heater supply sound wise. This can supply enough current for the demands of the 20B, but such a design can't be built for the 25A needed for the 304TL.... I really wish it could, but alas.......have to make due with what is possible.
JD
Each tube has to have it's own heater supply, they can not be shared as this is a two stage using DHT, where the cathode is also the heater/filament.
AC is said to sound good as a heater voltage supply( but can have a hum problem if not properly implemented), and series regulated DC less so, DC shunt regulation supposedly sounds better than series, and a Voltage controlled Current supply supposedly is the best DC heater supply sound wise. This can supply enough current for the demands of the 20B, but such a design can't be built for the 25A needed for the 304TL.... I really wish it could, but alas.......have to make due with what is possible.
JD
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