Metro-Loop Install B+ Supply

[metalhead3ecr]

I just bought two metroloop's to install in my builds. For this first amp these are the type of voltages I am reading and I just wanna know the best way to go about installing the supply for the loop board. MY B+ IS HIGH. I think I would need like 150k of 2W resistance if I went to that 504 VDC point (see pic). I feel like I would damage the loop board...

Not really looking to tweak my amp...I love the way it sounds as is. Can I just use the voltage after one of those 10K's ?

Here is a picture with the voltages I measured. https://www.dropbox.com/s/t6kwenxahdsik ... 1.jpg?dl=0

[metalhead3ecr]

Actually now I'm worried because the two big blue filter caps (one F&T, one ARS) are only 500VDC rated i think....and certain terminals are seeing 504VDC when on...

[danman]

What amp are you installing the loop in? 50 watt or 100 watt? Are you measuring voltages with tubes installed? Depending on the circuit, the caps could be wired in series or parallel. Need more info.

[metalhead3ecr]

they are both 50 watt amps. Tubes installed. I let the amp sit for 2-3 minutes and warm up and then took my measurements again. That 504VDC turned to 488VDC (I just did a proper bias too which may have caused this...both EL34s read 35mVDC on pin 1 now).

I should be ok with Cap voltage...although in the future I may want to parallel some filter caps to increase the voltage rating.

BACK TO THE LOOP:

is 488VDC still too high? should the bias come from a lower point on the board (like after one of those 10k's?)

[SDM]

Sometimes the B+ supply is wired differently in different Marshall layouts. With respect to those series decoupling /dropping resistors, your amp is wired "opposite" most others, hence the proper attach point for the loop B+ resistor is the 342V end in your amp.

In the link here: https://drive.google.com/file/d/0By1xsH ... sp=sharing
The three green circled points in the pic are all the same electronically, you can use any of them for the loop resistor/wire run in your amp. Use whichever is most convenient in your particular loop install.

[metalhead3ecr]

Thanks! That was exactly the answer i was looking for i will try and get it installed this weekend

[metalhead3ecr]

The loop works, but I get a weird tail end distortion that I do not like so much...any ideas? My B+ on the loop board is 310VDC
Here is a clip where I turn the bypass on and off.

https://www.dropbox.com/s/m4h7dszxfydrj ... M.mov?dl=0

[metalhead3ecr]

Nevermind, V2 was going bad, swapped it out and all is well!