Matchless/Bad cat build thread

[norburybrook]

update: After swapping the 5M1 bleeder for a 220K I've had some intermittent issues over the last couple of days. Amp would suddenly make a horrible noise and cut out, the pilot light(fender style 6v from heaters) would go off when this was happening to. I'm sure this is just a coincidence but it started after i did this soI've taken the rectifier board off and re done all joints. I've reflowed the half/full power and SS/Tube switches. reflowed the fuse switches.

I cannot make the amp do this by chop sticking anywhere and it seems very random. It makes no difference if I'm on SS or Tube rectifier. strange and annoying little problem.

any ideas anyone?

I've got a pair of old Mullard EL34's in there that are sounding great cathode bias means no need to worry about matching I've had these tubes for years. just odd ball El34's .


M

[martin manning]

Amp would suddenly make a horrible noise and cut out, the pilot light(fender style 6v from heaters) would go off when this was happening to.

So either something in the the heater circuit is shorting, or going open, or all of the power is going out. Do you know if the heaters go dark too? If the rectifier heater goes out too, it's on the primary side of the PT.

update: After swapping the 5M1 bleeder for a 220K I've had some intermittent issues over the last couple of days. ...It makes no difference if I'm on SS or Tube rectifier. strange and annoying little problem.

This says it's nothing to do with that resistor swap.

[norburybrook]

Amp would suddenly make a horrible noise and cut out, the pilot light(fender style 6v from heaters) would go off when this was happening to.

So either something in the the heater circuit is shorting, or going open, or all of the power is going out. Do you know if the heaters go dark too? If the rectifier heater goes out too, it's on the primary side of the PT.

update: After swapping the 5M1 bleeder for a 220K I've had some intermittent issues over the last couple of days. ...It makes no difference if I'm on SS or Tube rectifier. strange and annoying little problem.

This says it's nothing to do with that resistor swap.

I'm not sure if the heaters go out as they're at the back and pointing down when it's out of it's case. I'll remove the valve covers and flip the amp so I can see better. It's really sporadic though. I'll try poking the heater wires again to see if I can make a noise.

edit: well it's been on all day now and only done it twice early on and it's been lovely and well behaved the last 4 hours. I'm thinking I might take all the tubes out and get the air duster in there as it could be a bit of solder or something got in somewhere, perhaps movement caused something that had dropped down to short slightly. Just a thought.

M

[10thTx]

A couple of thoughts ………………………. may or may not be helpful?

I've had an amp make a horrible noise and then no noise before. The tubes were redplating and the oscillation would eventually cancel all the sound. IF I played the amp softly at a low volume, it would be fine. Soon as I pushed and cranked the amp, it would redplate. New tubes resolved the issue & nothing else was needed.

Do you know what the heater current rating is on the PT? Any chance you're at the limit or over?

Have you tried 6L6's or 5881's in the amp? They draw less heater current.

With respect, 10thtx

[norburybrook]

A couple of thoughts ………………………. may or may not be helpful?

I've had an amp make a horrible noise and then no noise before. The tubes were redplating and the oscillation would eventually cancel all the sound. IF I played the amp softly at a low volume, it would be fine. Soon as I pushed and cranked the amp, it would redplate. New tubes resolved the issue & nothing else was needed.

Do you know what the heater current rating is on the PT? Any chance you're at the limit or over?

Have you tried 6L6's or 5881's in the amp? They draw less heater current.

With respect, 10thtx

that's a thought. it's an AC30 transformer I'll check the specs. It would normally drive 4x EL84's at 100%


M

[norburybrook]

I've tried 2 sets of tubes. I had EHX and now have vintage MULLARDS

M

[martin manning]

EL84 Ih is 0.76A, so 3A for 4. Should be fine for two EL34's at 1.5A each. Pa max is 12W for each EL84, so you are very close there too.

[norburybrook]

the transformer I have is rated at 6 amps for the heaters so plenty


Pri.: 0-115V-230V-240V (50Hz)
Sec.1: 560V C.T. @ 160mA
Sec.2: 6,3V C.T. @ 6A
Sec.3: 0-5V @ 3A
Made in Europe


M

[pdf64]

I don’t think that a bad connection in the heater circuit would cause, per se, a horrible noise. Rather they tend to be characterised by a noticeable fade out / in of signal.
To me, that combination of symptoms may indicate a bad connection in the PT primary / mains circuit.

[norburybrook]

I don’t think that a bad connection in the heater circuit would cause, per se, a horrible noise. Rather they tend to be characterised by a noticeable fade out / in of signal.
To me, that combination of symptoms may indicate a bad connection in the PT primary / mains circuit.

yes, hence me re soldering the mains and fuse ( the primaries) connections but also the main rectifier board and tube rectifier valve connections ( secondaries)

intermittent issues are the worse things to solve

the amp is back in its case now so I will try again Monday to see how it behaves.


out of interest, does it matter which way the PT primary connections are wired in regard to live and Neutral? the PT has the leads labelled 0 and 240 so I've always wired the 240 as the 'live' and the 0 as neutral, but would it matter if they were switched as they're 'relative' to each other ?

M

[norburybrook]

OK, well here's a couple of pics and sound files of the amp.

I was going to put mesh over rear holes but gave up on that idea after this:

IMG_20200719_220458 (1).jpg

I was worried about the exposed terminals on the PT but actually in the case the tubes are in front of it so all good.

I got a logo made from an Ebay place cost about £6 for the 2 words. I think it's turned out well.

So here's a clean and a gain clip. Done naturally on a guitar I built myself , the Norbury Brook Telecaster Clean is the neck P90 and the gain is the bridge. Speaker is 1x12 Celestion Vintage 30 UK an old UK one not the new Chinese. Reverb/delay added after. Unusually I had the tone backed off a little on the clean but up full on the bridge dirty I added a bypass switch for the normally always on bright cap on the clean volume but in the sound clip the amp is with the bright in as per the original. It's also on Tube rectified for both tones. I normally like the SS for the gain but you can switch live so left it on the tube. I still need to make an AB box.

the settings are exactly as in the photo. The clean is loud so I had the volume backed off on the guitar, it's still not to bad though regarding hiss . As you can see there's plenty of gain still available on the gain channel, the level control is only at 10/11 O'clock and that's where the 2nd stage gain comes from.

IMG_20200721_131449.jpg

IMG_20200721_131523.jpg

Clean:

Gain:
(Mod edit: linked audio to directly play in browser)



M

[Phil_S]

Looks great, Marcus. Sounds even better. The clean clip is serene and quite pleasing.

[Colossal]

That sounds really good, Marcus.

[norburybrook]

Looks great, Marcus. Sounds even better. The clean clip is serene and quite pleasing.

thanks Phil. The clean on this amp goes straight from v1a to the PI so it's a very pure path, no tone stack. It's well balanced tough I find. It's bright so I roll back vol/tone for something like this. If that were in a band situation I might roll on a little more

I'm really pleased to be able to use my stash of old Mullard EL34's . They're all mismatched pulls so no good for fixed bias but on this amp they're perfect .

Forgot to mention tubes didn't I.

the 4x pre amp tunes are all bog standard JJ 12 AX7's the 2x EL34's are old Mullards.


M

[martin manning]

Fantastic! Love the tones and the logo. The latter is classy looking, and sufficiently sized for self-promotion from the back line.