Tweedle Dee, Take two

[fred.violleau]

Woke up this morning realizing that I had not grounded the input relay, so the switch is not working. Amazing how the brain works at idle and keep going at it... Will verify this in a bit, stay tuned

Fred.

[fred.violleau]

Confirmed, with proper grounding, cascading and Channel switching work as intended.
Now onto the biasing issue.

Here's what it looks like btw. Since I am waiting for the faceplates, I did not solder the din switch for the foot pedal. It's really a PITA to remove and redo just to fit in the plates...

PXL_20210419_121124794.jpg

Fred.

[fred.violleau]

Biasing sorted out, I was shorting my fixed bias current through the test points
No wonder power tubes were red plating

So now that everything seems to work properly, I will do a proper sound check tomorrow. It is late now and everyone is asleep.
With 120 VAC on the variac, I am now getting 433VDC on B+1 (loaded). All the other B+ voltages are now a bit too high.

So I will play with the amp and the variac so I can figure out which AC voltage I like it best. I may then try to reinstall the mosfet reducer with the correct drop diode.

Onto the next round !

Cheers,

Fred.

[rootz]

Good to hear Fred! What are your output tubes? This B+ seems a bit high for 6v6, even the JJ’s. Should be fine for 6L6 though. If you adjust your resistor dropping string, you should be able to get all your other voltages in line with the original specs.

Edit. I see you are using 6v6 power tubes. I’d lower the B+ a bit just to be safe.

Edit 2. Were you running cathode or fixed bias?

[fred.violleau]

Good to hear Fred! What are your output tubes? This B+ seems a bit high for 6v6, even the JJ’s. Should be fine for 6L6 though. If you adjust your resistor dropping string, you should be able to get all your other voltages in line with the original specs.

I setup the variac so that I get B+1 at 370, so it was fine for the 6V6s. But I was curious to see what voltages I would get with wall AC voltages, and ended up around 433 VDC which is way too high indeed for the 6V6s.

Edit 2. Were you running cathode or fixed bias?

I was running cathode bias.

BTW, a friend was reminding me the definition pf an expert... which is a guy that made all the possible mistakes Well I guess I am earning those stripes one at a time

Fred.

[rootz]

I like that quote! Reminds me a bit of a former professor of mine. He said the biggest difference between a professional and an amateur is that the former does not stop after making mistakes.

So in conclusion that would make you a professional expert.

What your power tubes can take with respect to plate voltage depends on the type too. There are many references to JJ 6V6S tubes running around 450V and doing fine. I have a pair of them in an amp with a B+ of around 420V and they seem perfectly stable and reliable. Pretty cheap too. Some say it is not a real 6V6, which might be (and is probably) true.

[fred.violleau]

So here is a quick demo of the rock machine this amp can produce in cascading mode. I am playing through humbuckers SD59 neck and JB on the bridge.

Sound capture is through the phone so apologies for you audio geeks.

The two switch in the front are as follow: the first one allows to choose normal channel or bright channel (this clip is solely on the normal channel) and the second switch activates the cascading of the normal channel into the bright channel (not paralleled).

Into he middle of the video you will hear me play with the switch in the back which are NFB (56k tap from the 8ohm PT) on and off as well as V2A cathode bypass cap on and off. Both have interesting effects on the sound (smoothing for the NFB when added and cathode caps in the circuit adds a fuller sound and a slight boost on the signal)

Plays through the 2x10 EVM closed back ported cab that seem to enjoy this little amp!

A little verb is on the FX loop.

https://youtu.be/bPTge7ycwhQ

Let me know what you think despite my rusty chops (had not played in a while before tonight...)

Fred.

[ChopSauce]

Bien joué Fred !

I guess the cascading is on par with this cab. I'm not sure it would sound as well when plugged into a speaker with a small magnet within a genuine tweed cab...
(& truely wondering, for your demo is pretty convincing)

[fred.violleau]

Hey @chopSauce,

Thanks! I did plug the amp into a celestion rocket 50 watt.
It sounds good too. A lot less efficient than the EV but stills good.
I will try and record something with it so you hear the difference.
The celestion can handle the beating with no problem.

Fred.

[norburybrook]

sounds great Fred I'm a fan of these modded tweed amps. I should build one with switches like this. I haven't followed the whole thing of late but did you wire the cascade thing different from the original ideas we did on the amps we made last year or so?

M

[fred.violleau]

Hey Marcus,

Glad you liked it. I did not change the way the cascade switch works. It is still basically the normal channel volume pot output that is being fed to V1B nstead of going into V2A. In order to tame the signal, there is a 680k resistor added after volume pot, before V1B for that route specifically. When the switch is not engaged, I keep the signal original, no attenuation.

All these switches are controlling relays and I have a 5 DIN plug ready to feed a 4 footswich pedal that allows to do what I do by hand, with my feet

I now have only one input and can switch from normal to bright channel without unplugging which offers great flexibility. It seems though that the switching is making a pop. I will try to see if I can make it quieter.

Fred.

[ChopSauce]

Hey @chopSauce,

Thanks! I did plug the amp into a celestion rocket 50 watt.
It sounds good too.

Thank you !

Don't bother recording it just for me, even though it is always a great pleasure to hear you sharing your enthousiasm with us...

[fred.violleau]

There you go @chopSauce.
Strat on a rocket 50 Celestion

https://youtu.be/5nE1KGKn0SY

Fred.

[ChopSauce]

Awesome!

Thanks Fred.
(I'm sold... )