Yes, but not very well, and you would be limited in terms of reservoir capacitor value which in turn would make the power supply unsuitable for UL operation.
12AX7 is perfect for 6BQ5, it was after all designed to drive it. 6BQ5 is a very sensitive tube and will not require more than about 10V to drive it.
12AX7 is perfect for 6BQ5, it was after all designed to drive it. 6BQ5 is a very sensitive tube and will not require more than about 10V to drive it.
A single 12AX7 and 2 full pentode EL84s most definitely has been done. Don't try wimpy 'X7 drivers directly into UL mode "finals".
The triodes in a 6EU7 are the same as those in a 12AX7. The "peculiar" pin out and spiral wound heater of the 6EU7 contribute to its low residual hum level, when heated with AC.
The 12AT7 is a very different "beast" than the 12AX7. The 'X7 is high plate resistance/low gm, while the 'T7 is low plate resistance/high gm.
IMO, the 12AT7 is a poor choice for duty in SE setups. The reason for that is its distortion spectrum distribution. OTOH, the 'T7 is wonderful in PP setups, where the net distortion spectrum for the entire amp is excellent.
Okay, are following statements true?
1.) You cannot successfully run a single 12AX7 into 2 UL EL84s SE, without solid state help?
2.) To run 2 EL84s in UL SE I need two preamp tubes to drive things?
Likewise.
Is there a preamp tube, 9 pin or otherwise, that has the juice to run a pair of UL SE EL84's?
As this is basically a scratch build I'm not strictly limited to the 9 pin. I'm intrigued by the UL. If it can work I'm game, otherwise I'm probably going to revert to a pentode configuration. Scared I'm gonna just burn up the SS parts and never get to sound.
Sorry I'm so thick with the clarifications. You feel I can get away with the 12AX7 without SS support to drive the pair of EL84s in single ended UL?
Also, that a switch to an ECC99 would be an upgrade, but unnecessary?
Thanks
Yes, one each triode of the 12AX7 can drive the grid of the 6BQ5 output pentode in UL with no issues.
The switch would be unecessary, and would also give you a much lower open loop gain so more distortion. ECC99 is mainly used in SET amps where the 300B needs a ridiculous amount of drive. Completely overkill and inappropriate for this application (even though I suggested it!).
The switch would be unecessary, and would also give you a much lower open loop gain so more distortion. ECC99 is mainly used in SET amps where the 300B needs a ridiculous amount of drive. Completely overkill and inappropriate for this application (even though I suggested it!).
Missed this earlier, sorry I'm technologically challenged. I'd hate to have to ask my 18 year old son how to Skype.
Yeah I think I'm gonna push through a clcrc power supply and some basic circuit topology and see what I get. I've always been better at fixing things that are broken than building from scratch.
You offered to draw up a basic non SS version of your EL84. If you're up to it I'd love to give it a shot.
Probly building with a new enclosure. Not sure by the time I strap on the new op trafos and choke that there will be much room to work. That and the enclosure is kind of bracketed together and not very sturdy.
I'm going to sort through what I have and make a shopping list and see what the budget looks like. That and looks like I might win a another Magnavox PP off ebay today so that will eat up some of my budget. Got to get everything selected and paid for before the wife checks the accounts.
I'm going to sort through what I have and make a shopping list and see what the budget looks like. That and looks like I might win a another Magnavox PP off ebay today so that will eat up some of my budget. Got to get everything selected and paid for before the wife checks the accounts.
Harlon, it's a constant current source with a decoupling capacitor improve power supply noise rejection. You can't really do it point to point and it's not so necessary in the simplified circuit.
Without it open loop gain is only reduced by a couple of decibels.
If you are going to build a new enclosure it might be worth getting an EDCOR power transformer to improve on looks, as well as safety.
Without it open loop gain is only reduced by a couple of decibels.
If you are going to build a new enclosure it might be worth getting an EDCOR power transformer to improve on looks, as well as safety.
Looks like I'm not gonna win the PP Magnavox so new Edcors all around are prolly in the budget.
With the new setup would you still suggest the same 3 units.
XPWR146 for power
CXC100-5H-200mA for choke
(2) GXSE15-8-5K for output
At one point you mentioned needed more than 5 Henry's of choke. Remember I'm from that American tradition of more is better.
When you are choosing a power transformer, more is generally not better, you want one with a heater tap, rated for about 2.5A and a 150+mA HT winding. If you choose a transformer rated for a higher current you run the risk of putting too much voltage on your heaters and significantly reducing the lifespan of your valves. However, an EDCOR rated for 4.5A shouldn't do any harm, maybe a slight increase.
I'd recommend:
XPWR146 (Probably the closest thing EDCOR has for this project)
CXC100-7H-150mA (The extra resistance will drop the voltage down to the 250V you need with the XPWR146, better smoothing also as the amp won't draw more than 100mA net DC)
I'd recommend:
XPWR146 (Probably the closest thing EDCOR has for this project)
CXC100-7H-150mA (The extra resistance will drop the voltage down to the 250V you need with the XPWR146, better smoothing also as the amp won't draw more than 100mA net DC)
There are all sorts of reasons for not using the 6CA4/EZ81, including the cost of a replacement. Save the tube for a future preamp project.
I'm uploading some "hen scratch" schematics that relate to my previous posts. The PSU assumes the power trafo already on hand will be recycled. I have not done all the "digging" needed to set some signal path parts values, sorry.
The PSU is slightly complicated and I'll explain why. It is fairly commonplace to bias signal tube heaters off B+, as a hum/noise control measure. Since the bias supply (C-) is derived from the 6.3 VAC filament winding, biasing off B+ is not available. Please notice that 1 side of the filament winding is grounded. Fortunately, the 1 A. of heater current reclaimed by eliminating the 6CA4 vacuum rectifier is quite sufficient to power both the bias supply and a 12 VDC heater supply for the 12AX7. Since we can't suppress hum 1 way, we'll suppress it another way.
Schottky diodes are called for in the negative voltage multiplier, for their low forward drop characteristic.BTW, Parts Express has a $16.88 special on soldering stations. The stock # is 374-100. Obviously, something this inexpensive lacks a temperature control probe in the tip. However, heat O/P level is adjustable. Somebody who only owns a simple iron would benefit by making the purchase.
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