Ihearmusic Posted March 29, 2019 Share Posted March 29, 2019 1 hour ago, RoHo said: another 50V for the cathode bias resistor The cathode bias resistor does not reduce the B+. I would work out the desired circuit first and then design the power supply most suited to the circuit requirements. Yes, the iron will be the most expensive part of your endeavor but it is also most crucial to the performance of the amp. You also do not want to find yourself heating up the inside of the chassis because you need to drop voltage. Capacitors don't like it hot. If your builder is competent in building valve amps, it should not be a problem for him to work it all out. Otherwise you might have to go and look for someone else. If he is a solid state man...........hmm! Link to comment Share on other sites More sharing options...
Digital Man Posted March 29, 2019 Author Share Posted March 29, 2019 (edited) Hi All, Many thanks for all of your most welcomed input and suggestions, my tech guy is definitely a tube guy but, he has only ever worked on and built valve guitar amps, I had him build me a fender champ clone, using a A&R power transformer that I found in my uncle’s garage and using one of the 6v6gt valves scavenged from the same radiogram as the aforementioned power transformer, it is rated at 5 watts and is single ended, I also used the perfectly good Goodmans Axiom speaker from the same radiogram for this fender amp, my goodness it rocks ! Edited March 29, 2019 by Digital Man Link to comment Share on other sites More sharing options...
Ihearmusic Posted March 29, 2019 Share Posted March 29, 2019 Good to have someone knowing his way around a Valve amp. I know it would be a lot quicker for your man to have a ready made circuit to build you the amplifier. It takes me a long time when I build something without schematics. A lot of testing, listening, changing, listening until one is satisfied. Not to mention the blowing out of the budget. Link to comment Share on other sites More sharing options...
Digital Man Posted March 29, 2019 Author Share Posted March 29, 2019 I have sent him some schematics, mostly for 6v6gt, 6l6, el34 and el84, I am also considering kt66 and kt88 circuits as well, we are trying to keep it simple and uncomplicated, we both agree that if I wish to have him build me a 45 set amp, then it would be best to start fresh with new components, so, to make things easier and to stick with my original request to make a amp using the chassis, transformers, valves that are on hand is the best approach 1 Link to comment Share on other sites More sharing options...
RoHo Posted March 29, 2019 Share Posted March 29, 2019 16 hours ago, Ihearmusic said: The cathode bias resistor does not reduce the B+. I was illustrating that with the given parameters the valves Vak maximum rating might not be exceeded. Vak is the limiting factor as I see it. That and the current rating of the power transformer. And I forgot to mention a further few volts drop across the output transformer. Link to comment Share on other sites More sharing options...
Ihearmusic Posted March 30, 2019 Share Posted March 30, 2019 2 hours ago, RoHo said: I was illustrating that with the given parameters the valves Vak maximum rating might not be exceeded. Vak is the limiting factor as I see it. That and the current rating of the power transformer. And I forgot to mention a further few volts drop across the output transformer. Plate disipation is the limiting factor and that is the product of a given plate voltage and plate current. Link to comment Share on other sites More sharing options...
RCAJack Posted March 31, 2019 Share Posted March 31, 2019 (edited) Regarding the power transformer, OP would need separate 2.5V windings for each 45 I believe? Plus a winding for the rectifier, and then another for whatever input valves are used. There are various methods of getting the required filament voltages, such as adding extra power transformers to the chassis. Also the eternal questions of whether you want AC or DC on your heaters, regulated v unregulated heated supplies, and using silicon in the signal path. FWIW the simple solution for an all one transformer would be a model like this: https://au.mouser.com/ProductDetail/Hammond-Manufacturing/302AX?qs=REJuxFWWMVVejtzLa6rMzg%3D%3D Edited March 31, 2019 by RCAJack Added details Link to comment Share on other sites More sharing options...
Digital Man Posted April 1, 2019 Author Share Posted April 1, 2019 Hi All, I am now going to change the title/heading of this thread to reflect the direction that it is now taking. Thanks. Link to comment Share on other sites More sharing options...
Digital Man Posted April 1, 2019 Author Share Posted April 1, 2019 Hi All, I have decided to change the heading of this thread to reflect the course this thread has taken, I bought a 1950's, I assume, HMV Radiogram over a year ago, I only had the electronics sent to me and the cabinet stayed behind, I originally purchased this unit to scavenge the parts to have a Fender Champ style amp made, which has been done, but, we did not use the power transformer from the radiogram as I procured another power transformer for that build, so, I thought that I could use the power transformer in a 45 SET amp, I could probably use this power transformer in the 45 SET amp build, but, to keep things simple and to use up as many left over items from the radiogram as possible, I will forego the 45 SET amp for now and revisit it maybe in the future, depends how this particular SET amp turns out, one drawback is that, I do not know who actually built this vintage power transformer, the radiogram was a 1950's HMV, I will add photos and maybe some one could tell me anything if they know, then maybe a data sheet for this power transformer could be obtained, which would be great ! Thanks. Link to comment Share on other sites More sharing options...
Digital Man Posted April 3, 2019 Author Share Posted April 3, 2019 Hi All, Okay, I have narrowed down my choices of which valves to use with this vintage power transformer, I may stay with the original setup, being, 6V6gt in SE, which will yield 4-5 watts, 6L6 in SE, which will yield 10 watts or EL34 in SE, which will also yield 10 watts, another way to go is SE UL with any of the three previously mentioned tubes as well and one can multiply the wattage by a factor of three against the SE watts given for each tube, for example, SE 5 watts translates to 15 watts in SE UL mode, I am assuming the the driver tube (as well as the transformer and circuit design) will be a greater factor in the overall sound character than the power tubes and I am assuming that the power tubes just does that, give you the power rather than significantly affecting the overall sound, please feel free to correct me if I am wrong or partly thereof. Thanks. Link to comment Share on other sites More sharing options...
RoHo Posted April 3, 2019 Share Posted April 3, 2019 Consider your speakers first. If they will be happy with only a few watts then I would go for one of the non-ultralinear circuits. A well designed circuit will sound better than a poor one regardless of tubes. Will a good EL34 cct sound better than a good 6L6? That's a really hard question to answer. Again, if your speakers are not limited by either circuit then I wouldn't expect a big difference. Sounds funny to say but valve amps and especially SE valve amps are more speakers than output tubes. Link to comment Share on other sites More sharing options...
Digital Man Posted April 3, 2019 Author Share Posted April 3, 2019 Hi, Okay, My speakers should be fine, I only have a small room to energise and I no longer play my music load, not even on the odd occasion, but, if I have to change my speakers, then I will, but that is a discussion for another time, for now, I prefer to focus on the amp, so, if I build either a 6V6gt SE at 5 watts or a EL34 SE at 10 watts, what could I expect to hear from the 5 watts to 10 watts ? Link to comment Share on other sites More sharing options...
Digital Man Posted April 4, 2019 Author Share Posted April 4, 2019 Hi All, I just read that a EL34 is the only 8 pin tube that doesn’t have the suppressor grid internally connected to the cathode, which makes it possible to wire the tube as a true triode for SET , interesting. Thanks. Link to comment Share on other sites More sharing options...
Digital Man Posted April 11, 2019 Author Share Posted April 11, 2019 Hi All, Considering that a 6V6gt as a set produces 5 watts and a EL34 as a set produces 10 watts, what, if anything, would the 5 watt difference be and/or produce ? and would it be worth the effort to have those extra 5 watts with the EL34 set ? Thanks Link to comment Share on other sites More sharing options...
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