Ever since I sold off a Jeff Larsen 2A3 amp ( still smarts!) as too light weight on Bass ( rookie thinking!) I found Mr King's brute 6B4G --- an amp with the qualities of a 2A3 with the power to do some bass...... since then I have been focused on keeping "tube history" alive and present .....
Tulsa is a music town with lots of history...... making music and playing music..........there is also the history of listeners--- the music fans---that were devoted to hearing music as played .... as best we can!
Tulsa is a music town with lots of history...... making music and playing music..........there is also the history of listeners--- the music fans---that were devoted to hearing music as played .... as best we can!
Oh, one more thing , Big Shout OUT! to Blind Lemon! You just keep piddling !
Takes a dead amp on vacation!! Gotta love that!!
Takes a dead amp on vacation!! Gotta love that!!
The output sound of push-pull tube amplifiers may depend more on phase splitter circuit. .Cascode in some pushpull amps has good results even in drive single-ends. Look at f2a se Ampfire ..... design by Ken Shindo in Japan. A cascode with 6aw8a..... I drew cricuit and made , the sound is unbelievable .
Update on the Stellavox 6B4G amp:
Be damned if the 6DJ8s didn't work. ;^) Bad thing is those Rifa coupling caps were leaking DC so for the time being I stuck in some ODs to get this thing working right. (any suggestions on maderatly costing coupling caps to replace the ODs) We had some straight sided Sylvania 6B4G and some coke bottle (3 Raytheon/1 Sylv). I put the straight sided tubes in and some 6DJ8s in and it sounded pretty good except for the really bad hum.
Recapped it with new electrolytics and that helped but still had some hum. Got to screwing around with it with different things, longing for a possible GL, no luck. Just to try something else I swapped the DJ8s out but no luck. Swapped out the power tubes for the coke bottles and bingo. Still a faint hum but perfectly acceptable.
Can anyone explain that??? I mean it hummed equally bad on both channels.
I am waiting on a couple of 100v/100uF axials and it will return home to Okietube.
BL
Be damned if the 6DJ8s didn't work. ;^) Bad thing is those Rifa coupling caps were leaking DC so for the time being I stuck in some ODs to get this thing working right. (any suggestions on maderatly costing coupling caps to replace the ODs) We had some straight sided Sylvania 6B4G and some coke bottle (3 Raytheon/1 Sylv). I put the straight sided tubes in and some 6DJ8s in and it sounded pretty good except for the really bad hum.
Recapped it with new electrolytics and that helped but still had some hum. Got to screwing around with it with different things, longing for a possible GL, no luck. Just to try something else I swapped the DJ8s out but no luck. Swapped out the power tubes for the coke bottles and bingo. Still a faint hum but perfectly acceptable.
Can anyone explain that??? I mean it hummed equally bad on both channels.
I am waiting on a couple of 100v/100uF axials and it will return home to Okietube.
BL
Do you know for sure that the Sylvanias were well-matched? I've never seen a straight-sided 6B4G, can you post a picture? The output tubes have to be well matched in this amp or it will hum.
Hi Hooman,
I am interested in the Shindo amplifier. Do you mind to share your final circuit?
It looks like you are driving f2a tubes, which have low bias voltage. Can the driver be revised to provide more swing? I have a hard time to find the triode curve for the pentode section for a quick estimate.
I have the circuit of f2a amp. And I have built it several times. The bias is -10V. The power supply is+ 350V and the output is 10W. After a few years of studying on Shindo's products, I made several models. I never seen one of them.
GG: to be honest I do not know how well they are matched, that would be a question for Okietube. He took the tubes back with him the other day.
I saw a quad of matched for $2k on ebay.
BL
I saw a quad of matched for $2k on ebay.
BL
Ah, those are the triode-wired 6AV5s that were sold to the military as latter-day subs for 6B4Gs. Since they are indirectly heated, there wouldn't be any filament hum, so it must have been very poor matching.
Found several offers for 6S4S new old Russian made... rated as best sounding (???) still in the $50 plus not offered as matched just new ....but is the issue AC/DC or tube quality.......
Common mode noise in a push-pull amp cancels out provided the output tubes are very closely matched. I would not put DC on the 6B4Gs, myself. What is the hum now, 60 or 120Hz? You might still have some residual ripple, or the input stages might have poor power supply rejection. Hard to say without a scope.
Today, a tube amplifier should not have hum. They can be heard in the silence of the room. It is better to use DC for filimant in dht tubes. This is very simple.
You need 6-a diode bridge and two capacitors of 10,000mf-10v. Don't bother yourself. Pairings dht tubes is not an easy solution for hum in amp.
You need 6-a diode bridge and two capacitors of 10,000mf-10v. Don't bother yourself. Pairings dht tubes is not an easy solution for hum in amp.
Don't you need a higher current rating on the secondary for a bridge rectifier? The ST-70 power transformer is already marginal as it is.