Nice Useful Mod for My Chihuahua

[syscokid]

Two and a half years ago, I assembled an Allen Amp Chihuahua KIT. 6 watts, 6V6, Reverb, 10" speaker combo, based "loosely" on Fender Blackface Champ. The amp has a way oversized output tranny, and can be operated with a 6L6 to produce 10 watts. But to properly switch over to the 6L6 from the 6V6, I would have to remove the chassis and replace two power resistors and switch by reconnecting the output trannies impedance leads.

I recently found out that David Allen has updated the design by implementing a control switch to simplify the process of switching between a 6V6 and a 6L6. I contacted him, and he offered me a very nice and thought-out upgrade kit. All I needed to do is remove the backplate, add a switch, add a resistor, add some wires, and cross my fingers.

Zee parts, with layouts and schematics:

The only parts that I didn't need was the brown ohmite resistor and the jack. Didn't really need the tube either, but it's nice to have some backups!

Done...:



The backplate makes it all look righteous...



So instead of originally taking about 30 minutes to switch the type of power tubes, now it takes about two minutes and a little hot pad, ha ha!

 

[Sp8ctre]

Two and a half years ago, I assembled an Allen Amp Chihuahua KIT. 6 watts, 6V6, Reverb, 10" speaker combo, based "loosely" on Fender Blackface Champ. The amp has a way oversized output tranny, and can be operated with a 6L6 to produce 10 watts. But to properly switch over to the 6L6 from the 6V6, I would have to remove the chassis and replace two power resistors and switch by reconnecting the output trannies impedance leads.

I recently found out that David Allen has updated the design by implementing a control switch to simplify the process of switching between a 6V6 and a 6L6. I contacted him, and he offered me a very nice and thought-out upgrade kit. All I needed to do is remove the backplate, add a switch, add a resistor, add some wires, and cross my fingers.

Zee parts, with layouts and schematics:
View attachment 42169
The only parts that I didn't need was the brown ohmite resistor and the jack. Didn't really need the tube either, but it's nice to have some backups!

Done...:
View attachment 42170


The backplate makes it all look righteous...
View attachment 42171


So instead of originally taking about 30 minutes to switch the type of power tubes, now it takes about two minutes and a little hot pad, ha ha!

Love the mod! Quality work right there!

My Tweed Champ Clone has that ability built in as well. It will also run a KT66.

 

[SG John]

Looks like fun.

Is that Ampeg tolex on the cabinet, or is that an Ampeg behind the schematic?

 

[syscokid]

My Tweed Champ Clone has that ability built in as well. It will also run a KT66.

I've never have played through an amp with KT66's! Hmmmmmmmmmmm…

 

[syscokid]

Looks like fun.

Is that Ampeg tolex on the cabinet, or is that an Ampeg behind the schematic?

Good eye… Ampeg tolex on a Fender style cab with a 10" speaker:

 

[Hackmaster]

Very nice mods.
It truly is a fully equipped Chihuahua now.
Just like this one on the website.

 

[eSGEe]

 

[eSGEe]

 

[syscokid]

As I've been recently into molesting my Chihuahua, I decided to add a soft-start inrush current limiter for the Chihuahua's power supply, which is a topic I brought up in another thread. Also, I decided to finally move a couple of grounding points off the power transformer's mounting bolts. I can't remember where I might have read about not grounding at the mounting bolts for the trannies. Anybody have more info on this?

Anyways... 220 ohm thermistor installed between fuse and the PT's primary wire:



Heater center tap, "choke" resistor, and rectifier diodes were grounded at point #1. The earth ground was originally at point #3:

 

[ivan H]

I only just saw this thread, nice mod & great work as usual Sysco. Really wish David Allen did exports, I'd most likely have one of his designs. Regarding not using PT mounting bolts as ground points, the PT's laminate stack forms a great big magnet that is alternating north & south at 60Hz, & the mounting bolts, well think of the pole pieces in a humbucker in that they focus the magnetic field from the end of the poles towards the strings. I'm sure you can figure from this why we shouldn't use PT mounting bolts as ground points. Cheers

 

[BFT Gibson]

Nice amp !!

don't have a chihuahua but i do have a new friend..meet "Got" the goat..started calling him when i take my run...he slowly started to respond to my voice..now he runs up & likes to just hang out....then he follows to edge oof fence when i leave..he hears me start calling him as i approach..he comes storming over ..nose on that fence...

 

[syscokid]

I'm sure you can figure from this why we shouldn't use PT mounting bolts as ground points.

Unfortunately, I can't figure it out. Wild guess: Grounding at the PT mounting bolts could introduce AC hum?????

 

[ivan H]

Grounding at the PT mounting bolts could introduce AC hum?????

That's it exactly. Cheers

 

[syscokid]

That's it exactly. Cheers

I WIN, I WIN!!!! YEE-HAW! What do I get? "A baby's arm holding an apple"?

 

[RVA]

Great work Sysco. You have certainly "arrived" in the amp building world

 

[syscokid]

Great work Sysco. You have certainly "arrived" in the amp building world

Thanks RVA. Really appreciate the compliment. But I try to make it clear that all I do is copy-copy-copy. I would consider myself as an assembly worker... a very slow assembly worker. But, it's a lot of fun and extremely rewarding building these creatures. Especially when they work! Which also reminds me...: I haven't got zapped in a whole year...

 

[JohnnyGoo]

Nice work Greg.

 

[syscokid]

As a follow up with the results of adding a soft-start inrush current limiter to this amp: With my meter connected, I can clearly see a much more gradual buildup of DC voltages just before the first filter cap. Without the thermistor, immediately after flipping the power switch to on, full voltage is hitting the caps. For a couple seconds, I saw the voltages of around 10% to 20% past the normal operating voltages before settling down. With the 200 ohm thermistor installed, in about a 10 second time span, there was about half the voltages initially and from there it was a linear climb to the proper operating voltages. This has to be better for the amp's internals, right?

Another result from adding a thermistor is a 2% to 4% reduction in the B+ voltages. The Spiffy amp lost about 5 to 10 vdc. I installed another thermistor, this time in my Chihuahua amp, and it lost about 15 vdc. Very minimal losses and I cannot tell the difference if the amps performance has changed any.

EDIT on 4-27-20: I MEANT TO POST THE ABOVE INFO AT MY OTHER AMP THREAD:

Amp Mods for Better Reliability & Protection

The mod I want to try is called and Soft Start Inrush Current Limiter. Seems to be an easy and inexpensive mod. What does it do? It gives "the rectifier and power supply components a "soft start". It limits the cold start inrush current as the rectifier charges the filter (reservoir) caps. It is...

www.thetonerooms.com

 

[ivan H]

Did you check the 6.3VAC (3.15VAC a side) filament supply to be sure it's in the acceptable range? Cheers

 

[syscokid]

Did you check the 6.3VAC (3.15VAC a side) filament supply to be sure it's in the acceptable range? Cheers

Look at you... your always thinking... . Glad you mentioned it, because I didn't even think about checking the heater voltages! But I will check tomorrow. Thanks...