New EF86 Special build

[sixstringer]

Yes, these are the voltages I used to compare with my amp in the previous post. They seem to be close enough to me, I don't see that the original amp (meaning Mat's) has "substantially higher voltages". 10thth, didn't you build one of these circuits?

[10thTx]

Yes, I built a similar version of it and used a 5879 instead of EF86 and a 6V6 instead of an EL84. I think those changes may have lessened the good tone from the amp design?

I thought it sounded good, but it didn't have the "oh wow" factor I was looking for. I eventually rebuilt it into the SoLow Watt.

With respect, 10thtx

[matt h]

(deleted)

[sixstringer]

Check out the sound files for the post SE EL84 Mini ODS PTP, this is the sort of overdrive I was expecting from this similar circuit.

[tele_player]

In those schematics, the Drive pot wiring looks wrong to me. I'd expect the wiper to go to the ef86 grid resistors.

Robert

[sixstringer]

That's interesting. I think you are right about the schematic, but... I have it wired like the layout which has the grid (pin 9) going to a 150k resistor and then to the middle (wiper) lug of the Drive pot.

[sixstringer]

SUCCESS! Robert was right, I tracked back through the OD drive wiring and discovered two wires were reversed. Once corrected, the OD channel has nice, sweet sustain. It sounds great with a little delay. Thanks everyone for your input, especially Robert. Now I'll try a version with 2 EL-84s, double single-ended so I can keep the SE cathode bias.

[sixstringer]

New Question: Mat mentioned in the original 86 Special thread that the tone circuit did not work correctly. I built mine to his layout and it does not work either. The Bright. Mid and PAB switchs seem to work correctly. So.... can you take a look at the layout and schematic and recommend a fix? I see that the bass pot is wired differently in other AX84 Hi Octane layouts.
Thanks in advance. BTW, this little amp is really fun.

[10thTx]

You can try this and see if this is helpful? You'll have to determine what value resistor to try on the PAB. I simply put 4.7M as a suggested starting place.

With respect, 10thtx

[sixstringer]

Wow, that's a lot different than Mat's 86 special or the other variations of the 101HRM preamp layouts I've seen, you completely eleminate the two 20M resistors? Sorry for being a noob about it, this is my first experience with a PAB switch. Thanks for your help and patience.

[10thTx]

That is how I have my PAB (pre amp boost) wired on my Tweed BluezMeister and I am happy with it. The 4.7M resistor gives a boost but not a boost that is TOO big of a jump in volume for my preference.

With respect, 10thtx

[sixstringer]

Rewiring the PAB switch to 10thtx's example brought the tone circuit to life, now all controls function with good range. I've done a little work on the cab for this new amp, photos to follow.
Thanks again for your help and advice

[10thTx]

Glad that worked out. Thanks for sharing the results!

with respect, 10thtx

[sixstringer]

I decided to add relay footswitching to the PAB and OD switches. In laying out the 2 switch relay board, I found that I might be able to make it a relay "stick" with the Cliff jack attached to the PCB and the whole board mounted to the chassis via the isolated jack. I will post the layout soon.

[sixstringer]

I added another EL-84 in parallel with the original one, it sounds great, I was not expecting such a significant improvement in the OD sustain. I like SE, cathode biased amps. The Eminence Delta Pro 12A arrived but it won't fit in the cabinet (bummer). With the Jensen, it seems to be on par with the volume of a Princeton.

The SS rectifier was relocated to make room for the relay stick. The relay stick has a 5v regulated power supply, two relays and the jack all in one.