EL844 Amp Based on 5f6a?

[M Fowler]

I have built the Rocket 6 or 7 different ways using EL84's, 6L6, KT66, EL34s and 6550's.

I built one with a Marshall plexi tone stack into EL34's but the board layout is all TW Rocket and Plexi MV.

I have built several 5F6a one a 4x10 tweed stock values and another with gain 1 and gain 2 using 6L6s.

Built what you want and see how it turns out.

[Zippy]

OK, no more posting, Steve.

Keep us in suspense and then surprise us!

[renshen1957]

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.

Hi New Steve,

As to current, the EL84 (760 mA) is hungrier than a 6V6 (450mA heater current), but a little bit leaner than a 6L6 (900 mA). Compared to other octal tubes which feed on 1.4 amps to 1.8 amps (written specifications, measured higher depending on tubes) the EL84 is a piker.

Fender amps weren't known for have a stiff, heavily filtered power supply.

I wouldn't judge the AC30 by a reissue, a Chinese Crxp model at that. Similar to the Bassman reissued of Fender and the Bluesbreaker reissue of Marshall, it wasn't an exact recreation/duplication of a classic amp, rather an attempt to quickly cash in on a market that boutique builders have proven to be lucrative.

The blanket over the speakers could be a number of factors. I would trade these out for Weber Blue Dogs for a start.

Let's just say that the AC 30CCs has issues and a bad reputation for reliability that is only exceeded by Bugera. Other than as complete rebuilds, gutting the interior and starting from scratch, I wouldn't touch them.

As to Tweed Bassman and Vox AC30's, I think you are comparing Apples and Oranges. The differences are more than the similarities:

1) The Bassman is a class AB fixed Bias with a NFB amp with 2 beam tetrode power tubes, and a B+ that is higher.

2) The Vox is a cathode bias class AB amp without NFB and 4 true pentodes (miniature versions of the EL34). The EL84 limit the voltage.

3) Both are considered to be the same output Wattage (contrary to advertising by Fender back in the day that claime the Tweed amp was 60 Watts), however an original JTM 45 Marshall is also in the same wattage category.

Among the similarities are:

1) The Output transformer primary in a Tweed Bassman is at 4 ohms and the Vox OT primary is also 4000 ohms.

2) Both amps use the same type of PI.

3) The Tone Stack for the AC30 is derivative of the Fender Bassman amp.

I've heard cathode biased 6L6 amps running in true Class A amps without NFB in which the 6L6 tubes sounded sparklely and very reminiscient of a true Vox AC30. I've built an amp with EL84s with a very Tweedy sound to it (among other circuit refinements, 10k ohm resistors grid stoppers on the power tubes.

The high current in the Power Transformer 6V3 heater taps by MC would be of very little utility in an amp fueled by the EL84, unless you plan to change out the iron at a later date for reuse after experimenting with the circuit.

The current would be of value if you were using octal tubes and with a simply connection of pin 1 to pin 8, you could have the option of using KT 66, 6CA7, KT 77, EL34, 6v6, 6L6, 6550, KT88, EL 90s, EL98, EL 100, EL 120 (I am not kidding) with bias adjusted to accomdate the tubes and an amp with 4 inch power tube centers to accomodate the larger tubes.

You might to look at what is available from www.edcorusa.com as to PTs and OTs for more options.

And the discussion hasn't started on the preamp circuity of the 5F6-A and AC30.

So it isn't the necessarily the tubes.

Best Regards,

Steve