Hi Bas,
My amp is a 6SL7 SRPP_2A3/45 with Hashimoto's. It definitely has a nice sound. However, owning several EL84, I have always wanted to build a simple SE EL84.
I would like to use the regulated HV P/S for G2 and VB408 is either unobtainable or seems not to be genuine.
Do you have two more pcs which you can sell to me?
Thank you a lot,
Marius
My amp is a 6SL7 SRPP_2A3/45 with Hashimoto's. It definitely has a nice sound. However, owning several EL84, I have always wanted to build a simple SE EL84.
I would like to use the regulated HV P/S for G2 and VB408 is either unobtainable or seems not to be genuine.
Do you have two more pcs which you can sell to me?
Thank you a lot,
Marius
I'm going to do just that with my RH KT120! But for this little critter I'll use the VB408's I have in my partsbin. They have been in my partsbin for more than a decade nowAnd I'm sure they felt unappreciated.
Hi Bas, can you describe how to install the VB408 as a screen regulator. I have been wanting to do some kind of screen regulation but most regulators are a bit cumbersome for a small SE EL84 amp. thank you for replying, cheers, 808
I'll have a look this weekend in my partsbin. If I don't have them I can send you some LR8.
Sure. If you look at the attachment. You can forget the diode and I left out the caps. Though perhaps adding the c2 would be better (they say in the datasheet that it will prevent ringing)
The in Vin connected to the b+. And the Vout to the screens.
I'll have a look a the R1/R2 in my amp..this weekend.
Attachments
Bas,
The effect of the diode is to "Protect" the available supply.
Sounds nuts I know, But if the regulator is connected to the B+ if the B+ sags it will pull down the voltage on the input of the reg. This may or may not be audible. So that's the combination of input cap and diode. If the regulation voltage is low enough then the supply wouldn't sag enough to have an effect.
Regards
M. Gregg
Thanks M Gregg.
Its OK as long as the voltage on c2 doesn't become greater than c1 because then it would reverse bias the reg. Obviously if the voltage across the reg was to go lower than the cut off the reg would turn off and on dependant on the supply voltage. But as you say probably not an issue.
(I would keep C2)
or some level of capacitance on the output.<<again the audible impact of cap type is worth a test.(just for fun if nothing else)Regards
M. Gregg
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Wonderful amp, despite what some forum contributors would have you believe.
I just finished an EL84 spud ('Yukon Gold') amp and can attest to the nice sound of a SE pentode with some feedback.
Hi Bas, thanx for the diagram. Now if I can find some of the regulators I will be a happy clam. BTW, how much current can this regulator handle?
I just finished a SEP EL84 w/5751 on a Zenith chassis using the original trannies. I built this using the Magnavox circuit (DCG version) and will it compare the sound to the other SEP RH84 based on another Zenith chassis. Both units have the exact same trannies so it will make for an interesting comparison. I couldn't make them exactly the same as I have different chokes but both have CLCLC power supplies. The new one is just breaking in and my first impression is that the sound seems a little more brittle sounding. I think it is from the GNFB. I am going to let it get about 50 hours of play time and put the RH84 up for a head to head comparison. cheers, 808
Hi from Greece! I built this amplifier and i use it every day! I use it 250v/200ma in HV section,ss rectifier,and CLC(200UF/10H/200UF) . The EL84 biased VERY hot I have 350v in the anode 340 in screens,and 38-42ma plate current. I have 3,3k resistor in screen,an 300 ohm in cathode,only these change from original schematics.I test amplifier with nomimal ratings ,but the sound it is not the so good!I use james transformers and the sound is impressive full bass,and dynamics,very good middle,especially in women voices,and very good highs! It drives my 89db/w wharfedale speakers without problem. I test many EL84 tubes,because biased very hot,and i have many problems!! Here the results: Russian 6p14p-ev,no problems at all,very good sound,NOS valvo el84 very good sound but after a few hours arced inside,fast death.shuguang el84 i like the sound of this tube.I used chinese tube few months,black stains like mullards,but i have thermal runaway in one tube. JJ el 84 no problem at all,but i dont like the sound too many middles,toshiba el84 not heavy bass,very good middles and highs,not to my taste.In this time i used polam el 84,very good tubes,and sounded marvellous,no problem at all,the best el84 ever!In preamplifier i use RFT ECC81 best sounded tube and dirty cheap! The EL84 tubes sound marvellous in about 320-350 volts and biased at 100% of anode dissipation,i cant explain this!I suggest this version of rh84,but needs attention and use high quality el84 tubes,like e84l nos or 6p14p-ev russian.I not like semiconductors in this circuit,no good sound at all. I test variation with ccs on cathode and zener in screen in output tubes,harsh sound,not good at all I use semis only on power section,because i can use large capacitors,lower ripple and more dymamic sound with out shag of tube rectifiers.Bye!
Hi everyone,
I'm writing to say that Bas is right. I built a breadboard EL84 SE (250V on plates, 242V on G2's) and with regulated voltage on G2's the sound is very articulated and relaxed. This is a very nice little amp and I want to thank Bas for the pair of VB408 and for his great suggestion.
Iron is James 6123, tubed p/s and only MKP except 10 uF just before triodes.
Wish you all a happy 2016 with great finalized projects,
Marius
I'm writing to say that Bas is right. I built a breadboard EL84 SE (250V on plates, 242V on G2's) and with regulated voltage on G2's the sound is very articulated and relaxed. This is a very nice little amp and I want to thank Bas for the pair of VB408 and for his great suggestion.
Iron is James 6123, tubed p/s and only MKP except 10 uF just before triodes.
Wish you all a happy 2016 with great finalized projects,
Marius
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