Sunday, 27 April 2014

What a Difference a Valve Makes

Got a Mullard ECC83 off Mr. Foxen to try in the Blackstar HT-DistX he traded me. It doesn't "completely open up the EQ" as I've seen claimed on the interwebz about replacing the valves in the HT pedals (a pox on over exaggeration), but it does make the gain sound nicer which is a big plus.

Now follows some gutshots and notes.

Fuck your warranties.

The immediately obvious thing when taking the boards out of the HT-DistX is that they're generic. Theoretically this means the pedal is very, very moddable. In practice it appears no bugger has even bothered and schematics are pretty much hen's teeth, so that's something to ponder for another time.

As on the other board there is a lot of space other components, including two more switches. Shown is the stock Sovtek valve

I had wanted to get the pot values as they would be the most immediately useful mod I could potentially make, but there are no values visible. I doubt these are particularly great pots, which makes it even more of a pain. L-R: Gain, Bass, Mid, Treble, 'Infinite* Shaping Feature**', Level.

*Not actually infinite.
**Possibly as in 'it's not a bug, it's a...' as I haven't found the point where it does anything awesome.

Tuesday, 4 March 2014

Retrovibe RVT-40

Well, it works perfectly! The sound is so much clearer and definitely a bit more Rick-like when I have the settings right.

Can't wait to test it at band volume.

I may do a recording at some point.

Saturday, 1 March 2014

Carlsbro PA60 Blues and Retrovibe RVT-40

The Carlsbro amp still isn't working. Having sorted the filter caps and the HT fuse (which it turns out needed to be slow-blow) the choke resistor (basically a great big resistor that sits between the power transformer and the rest of the circuit) is duff, smoking when the power's on and reading about twice as much as it is supposed to. Sigh.

I've also rewired my Retrovibe RV-4 to roughly approximate the wiring of a Peavey T-40 bass. Thus, Retrovibe RVT-40. I got all excited when I finished it and forgot to get a picture of the wiring, but here's the outside of the bass with classy-looking new knobs and a wee switch that does phasey stuff to the bridge pickup (in theory) and the T-40 wiring diagram.

Retrovibe RVT-40

I can't test that it works until tomorrow, on accout of it being quarter to eleven at night... but once it is tested I'll report back either in celebration or lamentation.

Sunday, 16 February 2014

Carlsbro PA60 - Power Up Test

New resisistor and HT fuse in, powe cord into amp, plugged into circuit breaker (safety first).

Power on! Light! Wheeee!

Check HT fuse, just to be sure, and it's blown with no valves in the amp.
New HT fuse = blown

Dodgy capacitor is the most likely culprit according to Foxen and sure enough there's a bit of white fluff by the vent on one of the filter caps, which means it's probably dead, and this is further borne out by a quick voltage test across the caps. Best thing at this stage is to do a 'brute force' recap, so that's more money to spend.

Bah. But learning is good.

Sunday, 2 February 2014

Plumbing the Depths

Retrovive RV-4 in C# standard -> Nine of Swords Burial at Sea -> Blackstar HT-DistX -> Peavey Firebass power amp -> Orange OBC 115

Sub. Ter. Ran. Ean

That is all.

Project: Carlsbro PA 60 Head

As mentioned previously Mr. Foxen of Ampstack has given me a Carlsbro PA 60 to work on.

Carlsbro 60 PA Front

From what I can tell from info-mining the internet this is a early-mid 70s model, probably a late Mk II. All other Mk IIs I've seen pictures of are point-to-point wired whereas this is on PCB, but I cannot find any reference to a Mk III so kind of assuming that at some point during the Mk II being in production it was changed to PCB construction.)

I have done initial solder refreshing and resistor testing. During the course of this testing I learned that sometimes resistors in circuit test at a lower ohmage than they are rated for and that by popping one end out of the board you can make sure they're sound. One of the resistors is duff (cheapo non-original, natch) plus the HT fuse has blown so that needs replacing. There was also a bodged in power cable which I've now removed.

Carlsbro PA 60 Guts

Pretty PCB

Next I'm going to clean up the valve sockets, pots, input jack, etc. and after that is powering up with no valves to check voltages.

Finally here is a bit of random human interest stuff. The amp was apparently built by Trev and tested by people who as far as I know exist only as initials.

Build and Inspection Label

Sunday, 26 January 2014

Things are afoot...

So, it appears to be all go here at Atomic Tangerine.

Not only am I soon to take on my second non-personal guitar upgrade, but I've taken on a project from Mr. Foxen.

The guitar upgrade is a simple electronics and pickups replacement for a dude who wants a bit more punch and versatility from his Epiphone SG. Pickups will come from IronGear.

The project from Mr. Foxen is a Carlsbro PA 60. Basically a 60 watt all valve amp head originally intended for PA use. Pretty much a win-win situation as I get to do more learning and Foxen gets more of his to-do pile finished.