EL844 Amp Based on 5f6a?

[The New Steve H]

I really wanted EL84s, though.

[The New Steve H]

I'm putting together a BOM. I just noticed the twin 40 uF filter caps on the Rocket power supply. I don't know what to make of that.

Isn't that somewhat...huge? The schematic I downloaded comments on it. Apart from what it does to the rectifier tube, won't it kill sag and sustain?

I'm wondering if I should put in a switch so I can take one of the caps out of the circuit. I guess it can't hurt.

[diagrammatiks]

you sure they aren't in series?

[The New Steve H]

I'll post the schematic to save aggravation. It has two 40 uF caps, a choke, and then a third 40 uF.

I don't know if EL84s suck huge amounts of current or what, but that seems like a whole lot of capacitance.

I compared it to the 5F6A. It's a total of 180 uF for the Rocket, to 88 uF in the 5F6A.

It also has a standby switch, which I don't want.

[M Fowler]

Caps are cheaper now then when the Fender 5F6A tweed amp was introduced.

The Rocket caps are parallel. The reason for more caps is better AC filtering and caps store voltage so less loss of voltage when the power supply is in demand.

The old 5F6a could use some improvements or did Marshall already do that with their JTM?

Mark

[diagrammatiks]

hmm 80 will be hard on the rectifier tube.

although, i just checked the gz datasheet and it lists the max as 60 so you could get away with 80.

you should try asking people that have done that build b4 how their rectifiers hold up.

[M Fowler]

The 5AR4/GZ34 can handle more then the 60uf listed on the specs.

Mark

[The New Steve H]

But don't I want loss of voltage, so I'll get compression? I like compression.

[sliberty]

When the Rocket overdrives, you do get some compression, and its cool. It is part of the smooth feel to the overdrive. And don't worry about the 80uF first filter - this design has been implemented by lots and lots of us, and it works. Oh yea, a guy named Ken has implemented it too I think

[renshen1957]

I don't know what gives the Voxes that sound. I just skimmed an Aiken Amps thing about the AC30 not being a true Class A amp, so I guess it can't be because they're single-ended.

Say what? You need to slow down if you hope to learn anything - the Aiken article is worth reading slowly a couple more times.

The AC30 is not single-ended. It's a push-pull amp that is running too high B+ to operate in Class A mode.

Arghhhhhhhhhhhh... I gave away the punch line.

Hi,

After the quiessence level is reached on the driven side of the power tubes, any additional current is pulled through the capacitor bypassing the power tubes cathode resitor (bias resistor); the other side of the circuit is no longer conducting, consequently the amp to slips into Class AB (about 23 Watts) from Class A (tubes on all the time).

Best Regards,

Steve

[The New Steve H]

I know it works. It's just that what I want to build isn't a true Rocket.

I guess I'll catch hell from the diehard cloners.

[sliberty]

Never listen to a die hard

If you really want to build a Bassman, build a Bassman. If it is too loud for your needs, add a VVR. As I mentioned, I've never built or played a 5f6a, but I have put a VVR on a JTM45, and it worked out well. I also HAVE built a 6G6-B with a VVR, and it works great too.

Not really clear what the controversy is. Build the Bassman stock as a starting point. Lay it out with a VVR in mind in case you decide to add one later. Build for 5881's, but make sure you have the ability to offset impedence in case you switch to 6V6's. You can always use (1) zener diodes, (2) preset VVR, or (3) different dropping resistors to account for the lower voltages that 6V6's prefer. There are lots of ways to make the variations viable. But start by building the amp that you want.

[The New Steve H]

It has to be EL84s, though.

I don't think there's any controversy. YET.

[sliberty]

OK then - build it. Get a PT that will provide the right sort of voltages for the EL84's, and git 'er done. If for any reason he Bassman preamp and the EL84 power stage are unhappy playing together, you can make adjustments later.

[diagrammatiks]

when you overdrive the power amp it'll sag and compress regardless of what the filter cap values are.