OK, thanks for that detail!
A gas reg will work the same if it's place in series as a fixed voltage drop (ala Leslie and others), or a series Zener will work. We've discussed this before. Personally, I'd rather see the grid bias circuit made adjustable so each tube can be individually set.
I understand, but screen voltage adjustment wouldn't be necessary if grid bias was made variable. Also, I'm not sure the exact voltage being delivered to the screens, but a pair of VR150 tubes would drop 300V. That should be close enough. A small string of Zeners could duplicate it more precisely, but they don't glow.
Noise isn't a problem for either approach if the circuit is properly designed. If I understand correctly, the purpose here isn't to clone the Bogen, but only to make use of these particular output tubes under similar operating conditions.Other versions of this type regulator (not necessarily Bogen) have frequently used a 6L6 for screen regulation. That would be my choice if it was deemed necessary to duplicate this circuit.
I am still on it, but it is not easy and I need to work too! Power transformers can be substituted with control transformers, which you can get for less than 50USD for a 400VA one, giving you 400V at 1A running in reverse, using the 120V output as a 120V input. Yes the current doubles in PPP, but with paralleling output transformers that should be no issue at all. What I am attempting here is to find workable solutions using cheaper and more available different use high quality 70V line matching transformers to be found on eBay for around 10USD a piece, instead of that very good quality Edcor or Hammond or Dynaclone outputs, costing several hundred USD to buy. Everything in Jamaica is very expensive because the rich avoid taxes or just do not pay them altogether and the government can't bother like the Feds in the USA to prosecute them for tax evasion and just decided to collect via import duty at customs. After all, the rich are bankrolling their campaigns at election time, so those lovely honorables, as we call politicians here, don't want to step on the toes of their contributors, so they make the general public come up with the shortfall in government revenue. If you do not want them to confiscate the item you want to bring into the country, you better pay what customs demands, or you can't carry it in and customs auctions it off to friends at government auctions. All that off an average income of 250 to 400USD a month. We pay 4 times the money for a half a gallon milk as you do in the USA, so you see it ain't easy living here...
Thanks Jack, but the DB130 amps use a dual triode as a screen grid voltage regulator, so I am aware of that particular issue.
We have the same problem in the U.S. It's been gradually sucking the life out of middle class prosperity for at least a couple of decades now. Cleary not as bad as your situation, but worse is coming. Anyway, I tested a decent size 70V line transformer several months ago, and the performance was very poor even with no DC current flowing. Almost anything designed for hi-fi will probably be better, even if it's on the small side.
No, I am using them for push pull, so DC core saturation is cancelled out. Some here suggested that 8k can work with 6AV5 or 6FW5, but those Speco T7010 are rated at 10W only, so I must parallel them to get like 20W or even 30W. Again, I can't do 300 to 600USD on output transformers, so I am researching. I hoped you may have had some measurements on the Speco, since you ran a test on some others as you said. What I can say is, I only was looking at so claimed HiFi 70V transformers, understanding the fact that 99% of them are not wound for good fidelity, but PA only. But I am embarking on experimenting with high grade, good quality +/-1dB 70V line transformers. I do not understand why audio outputs must be so insanely expensive to make. Yes, they require more care and precision winding them, but that little bit extra work does not justify their prices going into the hundreds of dollars versus multi output power transformers with multiple secondary windings... I think it is a rip off which is being exploited by the few winders for audio transformers left in the market. Hammond used to sell the 125ESE for 15W SE, which has a very good response on the lower 2K + 3K tap frequency wise, even so being entry level or guitar use mostly, for like 30USD 5 to 10years ago, than at 48USD end of 2023 and now it cost you almost 80USD a piece. If that is not greed and exploitation of a market, what is it then??? The Australians use old torrodial or R-core 12V Halogen lighting transformers with multiple 12V output windings on NON High End stereo as output transformers with very good results. At a 1USD an "output transformer" you can't go wrong, can you? Everyone everywhere is kind of pissed off about those outrageous steady price gauging increases on output transformers... I would not burden a 70Volter with a B+ of 400V, 500V or more, but the laquer on the magnet wire should hold up to about 360V without issues. I am not aware of low voltage insulation ratings of magnet wire, unless I am assuming too much. I think they use the same magnet wire they use for power transformers in audio transformers anyway, but at higher voltage they put insulation tape on each wound layer to assist with preventing inter winding arc overs at higher B+.
www.antekinc.com
Kindly remember, I am looking at 70V transformers for music distribution, not PA. They are on the datasheet listed as +/-1 dB from what I see about 50-70Hz all the way to about 18-20kHz. Those used to sell at a premium before they were discontinued. I understand your argument and if they are not working out good, I always can replace them. It is for a kitchen and another workshop amp. Call it like a console amp, they sounded pretty decent, for HiFi I have Fisher, HH Scott, Dynaco etc. It is just that since the RuZZia war on Ukraine the output tubes for those have almost quadrupled, so I am looking for a "daily driver" for shop, kitchen and yard, which can use 1-5USD tubes instead of those expensive more common tube. If it gets close to HiFi it is good enough in a kitchen when a mixer runs or a steak sizzles in the pan, or a shop with power tools running... I do own sand amps, but they are top of the line and I won't put them into my shop to collect dust from cutting, sanding etc. Hey, I am experimenting and trying to learn improvising, because the global trade will be gone one day and getting supply of anything will be not easy any more. Get ready, WW3 is coming because all those powers want influence and rule others...
Understood! I live on an island without any assets of interest to the powers to be and have some hope to make it through whatever comes.... I will edit it out since it was off topic... But I will look for a vintage car just in case, you still need transportation then...
I will check into it, but Antek better be affordable. Hammond just almost doubled its prices not too long ago...Antek has toroidal output transformers in 40W, 60W,100W sizes. 100W is 5K, good for PPP sweep tubes at Bogen's 600V. The 40W 6.6K would work for P-P at a lower B+.
Tube Amp Parts - Output Transformers - AnTek Products Corp