Yet another 6424 build started

[AnalogDok]

Hi Y'all,

I've ordered a donor AO-43 amp and went through my spares and have most of the parts on hand. I'm going to use Steve Luckey's S-6424 example for my build but I want to add a tube reverb to CH 2. I'd like to patch in a Fender Twin Reverb style circuit as I have all the parts including the 9AB3C1B tank and a matching tranny. I'm wondering where to splice it in?
 :think1:I presumed it would go in at the VOL1 and return at the shared connection before the V2 after tone.

Any help would be appreciated.

[vampwizzard]

youll need another three triodes no? two more tubes? why not a one tube reverb circuit?

[AnalogDok]

Can I do a one tube reverb with the 12AT7? And still use either the Hammond tranny or the Fender tranny, That would be fine.
Do you have a nice example of one and where best to plug it into his schematic?

That would be great. Thanks

[vampwizzard]

1 tube reverb thread in our "All Time Great Information": https://el34world.com/Forum/index.php?topic=7957.0

As far as where to tap and where to reinsert will depend on the preamp. Id assume both would come after the volume controls where the channels are recombined.

[AnalogDok]

Thanks for that link Vampwizzard. I had looked at it but not as thoroughly as I did this time. From what I think I understand, I can still swap an AT7 for the AX7 and get more drive. I also want to use a dual foot pedal that has a stereo 1/4" plug so a stereo cliff jack should work for the Trem and Rev on/off functions. I've only built 5 amps so far and modified a bunch so this is all still pretty new to me. I've never done a reverb before.

[sluckey]

Since you are not trying to keep to the original circuit, I suggest a slight mod to the Supro footswitch. This will greatly simplify your wiring and allow the use of a standard Fender footswitch such as this...

     https://www.tubesandmore.com/products/footswitch-box-fender-two-button-vibrato-reverb-vintage

If you build your own FS remember that the reverb wire in the cable must be shielded.

[AnalogDok]

Wow, Thank you Steve,

The drawing really helped. I was thinking I'd get a click or pulse or something if I combined them and was thinking caps to kill it but this is a lot easier to implement.
I have a couple of ON/OFF foot switches that I tested last night. I'll have to open them up to see if there is any shielding. If not, I have another expense...LOL...
I already busted my budget on Daco-ware/Bakelite knobs for this build.

I'm not building this as a exact replica circuit wise. I wanted the early Led Zep grind and Supro sound but didn't want a single purpose amp. Having Reverb on tap makes this a lot more fun especially with the tremolo. I plan on making a retro style combo cabinet to house everything in so having the vintage knobs makes it more fun and visually interesting. I have lots of red and black vinyl left over from a bass boat seat restoration to use. It's too bad wood prices have gone up 4x in the last 6 months tho. If I do a real nice job, the wife might allow me to keep it in the living room, otherwise it'll end up in the office with all my other amps. I also have a well broken in Rola Celestion G12-30 dated 1985 to go into this build.
I was also planning on using the AO-43 chassis to save $$.

Thank you for the drawing too. That really helps with this build.
Much appreciated.

[AnalogDok]

I decided to build the amp exactly as per Steve's drawing. Adding a tube reverb might not be the best idea. I can always use an outboard reverb.
Anyway, I drilled and staked  the turrets and started populating the board. I'm waiting on parts at this point.
I'm using F&T and Sozo and Orange Drop caps and Carbon Comp for all the 1/2 watt resistors. I buy 10 or 20 at a time to find the closest ones to the values I need. I went with Alpha pots as it doesn't seen to matter on past builds. Steve's build documentation is excellent so I should be able to make this work.

Thanks Steve.

[AnalogDok]

So far so good.
I used a Sprague Atom 35uf cap, is that OK or should I use 33uf? Does it matter?

It's a tight fit...

[sluckey]

Supro used 35

[PRR]

> Does it matter?

No.

Look at your other e-caps. -10%/+30%. So a "33" could really be 30u or 43u. Anyway I bet (without looking) that anything over 25u is all the same here.

[AnalogDok]

I put fire in the bottles tonight.
The good, she started right up and both channels are operational.

Issues...
1. My voltages are high. A=368v, B=357v & C=303v. About 18v higher than on the docs. Pin 9 on the 6973 reads 363v.
2. Both channels (middle position) do not come on. Only individually. I'm using an ON/ON/ON switch.
3. Tremolo only works if the intensity switch is on and a foot pedal is connected but the footpedal does turn it on an off. No tremolo if I disconnect the foot pedal.
4. The Tremolo channel sounds weaker, bassy and a bit distorted. The tone knob doesn't have the range of the other channel.
5. The 6973 tubes are running a tad hot. I'm not familiar with these tubes so I don't know how they should look when running.
Any Ideas?

The good...
1. The non-tremolo channel sounds fantastic. beautiful.
2. The tremolo sounds wonderful. With the Tremolo channel turned down low, it is marvelous. I couldn't be happier with how the tremolo is working.

[sluckey]

Issues...
1. My voltages are high. A=368v, B=357v & C=303v. About 18v higher than on the docs. Pin 9 on the 6973 reads 363v. Not an issue. These voltages are fine.

2. Both channels (middle position) do not come on. Only individually. I'm using an ON/ON/ON switch. Not all ON-ON-ON switches are created equal. You must use a C&K 7211 and it must be wired like the schematic/layout.

3. Tremolo only works if the intensity switch is on and a foot pedal is connected but the footpedal does turn it on an off. No tremolo if I disconnect the foot pedal. Sounds exactly like you forgot the jumper between the sleeve and switch lugs on the FS jack.

4. The Tremolo channel sounds weaker, bassy and a bit distorted. The tone knob doesn't have the range of the other channel. It is a bit weaker. To fix the bass, replace the 35µF cathode cap with a smaller cap, 1µF to 5µF. The distortion is just the Jimmy Page effect.     Never noticed the tone control difference. May be normal. There is a slight circuit difference between the channels. Once you get the channel select switch sorted so you can run both channels, I bet you'll forget about these little issues.

5. The 6973 tubes are running a tad hot. I'm not familiar with these tubes so I don't know how they should look when running. Did you determine they are too hot just by looking at them? I didn't see anything odd. However, these tubes are made to run hot. My tubes were running at 24 watts which made me nervous since they are also expensive. I lowered the power to 18 watts with a resistor change. Look at the note on the schematic.

[AnalogDok]

Thank you for the lightning fast response.
1. Yayyyy...v = OK

2. I ordered and installed a DiMarzio 3-Position On/On/On DPDT Mini Switch. I'll get a C&K 7211 and see how that works out. The wifey really liked my tremolo demo this morning....

3.I'm using a Cliff Jack so the wiring is different than your diagram. I'll play with it some more today. At least it works.

4. I'll test my tube to make sure it is working properly. I bought new Tung-Sol preamp tubes and failed to test them before installing. Sometimes one side is weak. I actually used a  33uF cathode cap but I have other values to change to. What about changing the .0033 Mallory cap on the tone pot to a lower value. I'll hook up jumpers and experiment with different values.

5. The 6973 tubes have a glowing orange center element. I did install the 470 ohm 10 watt resistor to match your circuit change. They are unfamiliar tubes for me so running a little warm is probably normal. I don't like to spend all my Social Security Retirement on tubes either....LOL

The documentation was outstanding. It made this build go very well. Other than my dyslexic layout reversals and backwards heater wiring that I corrected, it went smoothly. Thank you Brother.

[sluckey]

I'd play with the 35µF cathode bypass cap before messing with the tone cap. Your cliff jack should be wired like this...

[AnalogDok]

I tried 8uF, 10uF, 33uF, 50Uf and 100uF. Nothing seemed to make any difference.
I went from .0033uF on the tone pot to 47pF and that seems to brighten and clarify it a bit.

Next are the channel and trem switching.

[AnalogDok]

It's all done and it's epic.
My switch has the same connects as the C&K so I wired it up as per the drawing and it works. The drawing you posted of the Cliff jack wiring worked perfectly. So everything works as expected and no issues.

I took her for a good long rip tonight. She was ridden hard and long with my favorite guitars and I'm impressed with everything she does.

Steve, you were right about the dual channel being amazing. It's easy to mix and get the exact tone you want. I run that 100% already. The Tremolo is incredible. It makes my Twin Reverb tremolo sound lame.
The amp is articulate but does have some bark and has some very nice distortion. I hooked it up to my pedalboard and was surprised at what it can do. It's my favorite amp right now and right there with my 100HDM with full SLO mod. It needs pedals to get it into high gain territory but it sounds fantastic nevertheless. Paranoid through my 4x12 with delay, Naga Viper and heavily modded Vintage Tube Monster was epic....

Thank you Steve...excellent build.

My next build is going to be a SLO-100 preamp on a Marshall 18 watt power section with tube rectification.

[AnalogDok]

 I thought you would like to see the finished product. It plays great and I use it both as a standalone to play really swampy stuff or it works really well with a Peavey RockMaster preamp.
It's an upside down copy of the Supro Magick Head with pearl white leather piping and stainless mesh in the rear to keep the booger hooks out. Matching Bakelite knobs and a violet jewel.