Looking for a Pentode wired El84 amplifier design. I have 2 5k opt and a small 200v power transformer i want to use in a little cool project. Is there any good schematics out there? 🙂
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Rh84
"RH Amplifiers: RH84 amplifier - revision 2" RH Amplifiers: RH84 amplifier - revision 2
"RH Amplifiers: RH84 amplifier - revision 2" RH Amplifiers: RH84 amplifier - revision 2
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I wonder how it will perform with such a small power transformer that i have. .Max voltage with a solid state rectified circuit is 275-280v .
How exactly small your small power transformer is?
You'll need something like 160-180mA rated secondary at least with the SS rectifier.
You'll need something like 160-180mA rated secondary at least with the SS rectifier.
Measure the secondary DCR - if it's like 60-70 Ohm or less, you're good.
If it's more than 100, I'd rather looked for another transformer.
If it's more than 100, I'd rather looked for another transformer.
I started looking at the schematics for the RH84. What values should i put on the pull down resistors? If anyone can edit a RH schematic for me i will be very grateful 🙂 🙂
Been a long day and its almost midnight here and im tired so i gave them a totally wrong name lol. . pull down resistors is something totally different.
The resistors between the power transformer and the tubes, that lowers the voltage going in to the the tubes i was thinking on.
After some google i found out that the The max voltage for El84 tubes are 250v ?
and the b+ in the chematics on the RH84 was 315v . And i have 275-280v out from my transformer. After rectification.
So i was thinking i maybe have to change the values on the resistors so that i don't get to low voltage. On the tubes.
The resistors between the power transformer and the tubes, that lowers the voltage going in to the the tubes i was thinking on.
After some google i found out that the The max voltage for El84 tubes are 250v ?
and the b+ in the chematics on the RH84 was 315v . And i have 275-280v out from my transformer. After rectification.
So i was thinking i maybe have to change the values on the resistors so that i don't get to low voltage. On the tubes.
Max voltage for an el84 is 300V. So you are fine with a b+ of 280. 280 - 12 =268 across the el84. 12 volt is the approximate voltage on the cathode.
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Historically EL84 despite their ratings were often run at plate voltages in excess of 400V particularly here in the U.S. The Russian 6P14P will survive this without issues, and is a good example of/replacement for a 7189 type.
If 300V and below I've found the JJ EL84 to be a good sounding choice.
In NOS all the usual suspects are good; RCA, GE, Telefunken, Mullard, Amperex, Philips (particularly the E84L)
If 300V and below I've found the JJ EL84 to be a good sounding choice.
In NOS all the usual suspects are good; RCA, GE, Telefunken, Mullard, Amperex, Philips (particularly the E84L)
So i can just build the RH amp without changing a thing. Take control measurements of the voltages and it will work perfectly? 🙂
Build as designed, test, and then adjust voltages only if required. There is pretty significant latitude as long as you are not over the tube's safe plate and screen dissipation limits. I imagine it will be just fine - it is a well proven design.
I have a good quartet of telefunkens - not NOS but low hours and test as new. I keep telling myself I need to build a small SE amplifier to use them.. My first stereo tube amp as a teen was a salvaged Magnavox with a pair of EL84, E83CC, and an EZ81 - it sounded pretty good. I've been doing a lot of solid state and hybrid stuff so no idea when I will get to it.
I have a good quartet of telefunkens - not NOS but low hours and test as new. I keep telling myself I need to build a small SE amplifier to use them.. My first stereo tube amp as a teen was a salvaged Magnavox with a pair of EL84, E83CC, and an EZ81 - it sounded pretty good. I've been doing a lot of solid state and hybrid stuff so no idea when I will get to it.
