Pleasant surprise - decent parts found!

[bugbear]

Just working to tidy up a guitar amp I bought, a Badger (of Leeds) "Downbeat" 30W.

Just measured the pos/neg DC rails at 35V. Main (axial) PSU smoothers are quite small at 1000µF, but are well rated at 50V, and they're Dubilier brand. All the other tone control and power amp electrolytics are rated at 63V and are by Samwha.

Shame they're all 85°C, not 105°C, but you can't have everything. All in all, a pleasant surprise.

As is usual in a guitar amp, some of the pots are scratchy, some of the knobs are damaged or missing, and various mechanical fixings are missing (3 screws in something with 4 screw holes...).

I think this will work out OK.

BugBear

PS: would uprating the amount of PSU smoothing capacitance be a useful thing to do?

 

[a.palfreyman]

Possibly. Depends if there is any audible 'hum'. Only drawback is that the inrush current will increase at turn on which could stress the transformer.

 

[martin clark]

Guitar amps play by entirely-other rules. What'd be a defect in a hifi system is all part of the 'character'. Weak PSU smoothing, to add to the break-up as it gets driven harder, and such things: def all part of such a playbook.

The hum content in use will likely be utterly-defined by the guitar pickup, cable choices anyway. Don't worry about that.

Don't fix that which isn't broken..

(yeah I've tried running my acoustic guitar mag pickup through the hifi ... nah. Too obvious I can't play... ditto with NS Wav4 upright I've had 15yrs ... but that tiny Roland Microcube, on 6 AA battteries - much fun!)

 

[bugbear]

I haven't traced the circuit (it all works, so not much motivation), but having checked a few component IDs it appears to be class B, quasi-complentary with diode biasing.

Very similar to this (which I saw on a Home Organ group today, by cooincidence)

Hammond 35 watt amp by plybench, on Flickr

 

[bugbear]

Here's an image of my guitar amp, with the track side mirrored and aligned, and the component side rendered semi transparent...

Badgering by plybench, on Flickr

 

[david ellwood]

I have an Impact valve head that hums like a boney M intro, wouldn’t have it any other way.

 

[bugbear]

I'm surprised it's got twin pos/neg rails (and a centre tapped traffo). I'd have thought a single power rail would be cheaper.

 

[PigletsDad]

I'm surprised it's got twin pos/neg rails (and a centre tapped traffo). I'd have thought a single power rail would be cheaper.

By the time you have put a large(ish) output coupling cap in, I am not sure there is much in it.

 

[bugbear]

Out of curiosity, I've started to trace the circuit. This is not helped by it using a pair of BC212 transistors, which are listed on the datasheet as having 3 options for pinout in the TO-92 package!!!

Last page...

http://www.datasheet39.com/PDF/493767/BC212-datasheet.html

BugBear

 

[glenn jarrett]

a few pics of a couple of amps i serviced for a friend re designed Marshall badge
20200123_145809 by glenn jarrett, on Flickr
20200123_132029 by glenn jarrett, on Flickr
20200123_145816 by glenn jarrett, on Flickr
20200210_135618 by glenn jarrett, on Flickr