V2a
Active member
Hi All,
I am currently building an amp with a 2 x EL84 fixed-bias output section and a 2204 (JCM 800) preamp. The OT is a Hammond 1650E - much beefier than most typical 18-watt offerings. The PT was supplied by Randy Fay (Phaez Amps).
Here are some photos of the amp as it stands. Actually it changed within 5 minutes of this photo being taken. The Presence control is out and has been replaced by another pot (to be wired up tomorrow).
Some miscellaneous notes:
- this amp is very quiet. I added an extra stage of filtering before power is delivered to the output tubes, so there is no power supply hum. The heaters are run with elevated DC (the orange wire in the photo, which carries ~70Vdc to the heater wires). End result: there is no heater hum.
- the long 10-watt resistor that is vertically oriented in the photo is in series with the output of the solid-state rectifier. Its a trick to add a bit of sag to this rectifier. The internal resistance of a tube rectifier is what makes it different from a diode rectifier, btw.
- The other long 10-watt resistor sits between the first two filter stages. Originally I had a 470R there, but it got toasty warm. Heat is the enemy of all electronic parts, and so I dropped the resistance to 100R. Now it runs much cooler. Fortunately the value of this resistor doesn't matter much.
- the dual-gang pot is a bootstrapped MV. It works well. But...
- In place of the Presence control, I will install a La/Mar PPIMV, at least temporarily. This will allow me to compare MVs in the same amp, but that is just a bonus. There is another reason I want to try adding the Lar/Mar in this prototype. I'll report on that later (at least if I find anything interesting).
- there is a lot of gain on tap. And on top of that, this thing is loud. For the Phaez fans out there, this thing runs on "Randy watts" - at the very least it runs with Randy's custom SIBLY power transformer. Good for 360VDC, which is more than enough for EL84s (the techs will agree with that statement).
- It's challenging to get a higher-gain EL84 amp sounding good, which is one reason they are rare.
- and on that note, I still need to fine tune the circuit.
- Randy Fay (Phaez Amps) provided the PT along with the initial schematic for this 18-watt variant. Randy has also answered several questions by email. And I bug Kevin O'Connor all of the time, and he is always quick to respond. Cheers to Randy and Kevin!
I am currently building an amp with a 2 x EL84 fixed-bias output section and a 2204 (JCM 800) preamp. The OT is a Hammond 1650E - much beefier than most typical 18-watt offerings. The PT was supplied by Randy Fay (Phaez Amps).
Here are some photos of the amp as it stands. Actually it changed within 5 minutes of this photo being taken. The Presence control is out and has been replaced by another pot (to be wired up tomorrow).
Some miscellaneous notes:
- this amp is very quiet. I added an extra stage of filtering before power is delivered to the output tubes, so there is no power supply hum. The heaters are run with elevated DC (the orange wire in the photo, which carries ~70Vdc to the heater wires). End result: there is no heater hum.
- the long 10-watt resistor that is vertically oriented in the photo is in series with the output of the solid-state rectifier. Its a trick to add a bit of sag to this rectifier. The internal resistance of a tube rectifier is what makes it different from a diode rectifier, btw.
- The other long 10-watt resistor sits between the first two filter stages. Originally I had a 470R there, but it got toasty warm. Heat is the enemy of all electronic parts, and so I dropped the resistance to 100R. Now it runs much cooler. Fortunately the value of this resistor doesn't matter much.
- the dual-gang pot is a bootstrapped MV. It works well. But...
- In place of the Presence control, I will install a La/Mar PPIMV, at least temporarily. This will allow me to compare MVs in the same amp, but that is just a bonus. There is another reason I want to try adding the Lar/Mar in this prototype. I'll report on that later (at least if I find anything interesting).
- there is a lot of gain on tap. And on top of that, this thing is loud. For the Phaez fans out there, this thing runs on "Randy watts" - at the very least it runs with Randy's custom SIBLY power transformer. Good for 360VDC, which is more than enough for EL84s (the techs will agree with that statement).
- It's challenging to get a higher-gain EL84 amp sounding good, which is one reason they are rare.
- and on that note, I still need to fine tune the circuit.
- Randy Fay (Phaez Amps) provided the PT along with the initial schematic for this 18-watt variant. Randy has also answered several questions by email. And I bug Kevin O'Connor all of the time, and he is always quick to respond. Cheers to Randy and Kevin!
