Next Build - RobRob Champ Micro

I'm having a ball trying to get my 5E3 working...not there yet, but that build should be done after I accomplish some troubleshooting. I have most of what I need to get started on the Champ Micro, so starting this thread!

For those of you that don't know, here is a page on the Champ Micro, with build details:

https://robrobinette.com/Champ_Micro.htm

It's basically a lower-volume 0.75 watt Champ with a Master Volume. Very simple circuit. I'm going to house in a Priceton Reverb chassis and head cab.

First basic question: the circuit calls for a voltage dropper resistor of 2W, 39k. I couldn't find 39k, so I bought 33k & 47k - what are the implications of using one of these instead?

Also, any tribal knowledge to be aware of while building this one? I'm going with the tube recto instead of SS.

 

@Lavochkin - how do you like the sounds of the amp?

 

@robrob - much appreciated

 

A couple more questions:

1 - I'm building in a Princeton Reverb chassis (widening a few holes, etc.). TONS of open space, which is a nice change from the 5E3! However, given the slant to the front control panel, the pilot light assembly touches the bottom of the chassis and flexes to fit. Is this OK, or will I have electrical issues? It LOOKS like the leads touch pieces of metal that are not the same as the "body" of the assembly that touches the chassis, but wanted to confirm. Given I'm using a standard Fender piece, I assume this is OK?

2 - The layout for the Micro Champ (below) shows four wires coming from the OT - blue, red, yellow, orange. HOWEVER, the OT actually has only blue, red & orange wires (no yellow). HOWEVER, it also has tabs 1, 2, 3, 4, 5, 6 on the other side of the OT. I'm guessing I attach a yellow wire to one of these tabs and that goes to the Speaker Jack (as shown in the layout). Looking at the specs for the transformer, this is pretty unclear...my guess, from the specs, is that I connect the yellow wire to BOTH tabs 1 & 5, then to the speaker jack, and this gives me an 8 ohm tap. Am I reading correctly? The table I'm referencing is shown below as well (last 2 images have data on OT).



Screenshot (9) by joelavely, on Flickr



Screenshot (13) by joelavely, on Flickr

Screenshot (11) by joelavely, on Flickr

 

Here is the on/off light - not the "fuse":

Untitled by joelavely, on Flickr

 

@robrob - looks like both the Hammond 1750A and the Classic Tone 40-18034 are unavailable right now. Hammond is out of stock everywhere (maybe issues with components from China? Just a guess) and the Classic Tone is no longer made. I could wait for the Hammond, but feels like a couple months. The other Hammond you list, the 125ASE, is around $50 instead of the $20 for the (unavailable) 1750A.

Any thoughts on what other OT will work? I am building BOTH a Deluxe Micro and a Champ Micro, but I assume they are interchangeable OTs. Mercury Magnetics?

 

@Paul-T - Amplified Parts has the Hammond 1750A, but the specs there say it is 22.8k:8 ohms, while different places on the Hammond site say the same thing in some places, but 25k:8 ohms in others!! Anyone know (1) does it matter and (2) has there been a change in the model and this now needs to be avoided?



Can anyone tell me the proper Heyboer model #? Or, is that just the Mojo Reverb Driver above? Weird, as it doesn't have the 25K:8 ratio...

How about this Weber?

https://tedweber.com/w022921/

 

Shoot - Amplified Parts is actually ALSO on backlog, needed to click on the order itself to discover. Back to the drawing board!

How about these Heyboers (I can't tell, as no spec sheets provided, so asking folks here if they have knowledge):

https://www.tubedepot.com/products/transformer-reverb-driver

No details given...


https://www.mojotone.com/amp-parts/Reverb-Drivers-and-Interstage-Transformers/Reverb-Driver

Mojotone says 29,000 primary on this one...not sure why, or if that will work?

 

I'm waiting on Tube Depot to confirm their transformer is 25k:8...any idea WHY I can't find a Hammond 1750A? I have tried everywhere I can, no one has them in stock. Is there a Heyboer that would work that someone actually has in stock? Feels wrong to pay $50 for a Mercury Magnetics version...

Is the Weber going to leave me wanting something better?
https://tedweber.com/w022921/

 

@robrob and others - The Hammond 270AX PT does not have a Center Tap wire (green/yellow wire in the layout above), so I need to create an Artificial Center Tap. Looking at the layout in Post #7 above, this would mean that, for V2, I am going to connect one 100ohm 1/2 Watt resistor from Pin 4 to Pin 8, and another from Pin 5 to Pin 8, correct? This connects both the filaments to Pin 8, which goes to ground. Just double checking before soldering.