Mofo

What people are working on at the moment
little eddy
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#16 Re: Mofo

Post by little eddy »

ed wrote: Tue May 12, 2020 3:33 pmI'm feeling quite smug at the moment.....somebody will knock me down shortly I'm sure.
Yes thank you Ed, and thanks for the bits to get me started on this one.

I'd better get round to tweaking my 41MP pre as I am sure Steve's will wipe the floor with it.
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
Cressy Snr
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#17 Re: Mofo

Post by Cressy Snr »

steve s wrote: Tue May 12, 2020 8:03 pm Sorry Ed alot goes on at Owston and mofo would have ment nothing to me at the time

I managed to find a suitable transformer this afternoon, I think its a partridge, perfect in every way except for the rectifier windings 4 or 6.3vt at 2 amps. I had to go back to find suitable rectifiers. I came back with a selection of possibles.. all subject to a test, one is a perfect match for the Mazda ac/p if it works
Fingers crossed.
Gotta love that rectifier. :D
Sgt. Baker started talkin’ with a Bullhorn in his hand.
steve s
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#18 Re: Mofo

Post by steve s »

little eddy wrote: Tue May 12, 2020 9:23 pm
ed wrote: Tue May 12, 2020 3:33 pmI'm feeling quite smug at the moment.....somebody will knock me down shortly I'm sure.
Yes thank you Ed, and thanks for the bits to get me started on this one.

I'd better get round to tweaking my 41MP pre as I am sure Steve's will wipe the floor with it.
I doubt it mike.. The valve I'm using is very similar to your 41mp sound wise. I can't imagine it being a lot different.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
little eddy
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#19 Re: Mofo

Post by little eddy »

What current are you running Steve? Do you have plans to increase when you have more voltage to play with?
TD-125/RB250/MC25FL & 'Snail' phono, NAS/SBT with CS4398 DAC, 41MP pre & MoFo Power, still messing with OBs.
steve s
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#20 Re: Mofo

Post by steve s »

I set it to 1.6 volts. I've ordered some 19vt computer supplies to ensure the distortion is low where I want to use it, should have those in a couple of days along with the small chokes for the front end.
I started assembling the front end last night. Hopefully testing by the weekend.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
steve s
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#21 Re: Mofo

Post by steve s »

The power supplys came on Saturday along with the power supply chokes.
Got a few hours in on Sunday and this afternoon.
A few issues.. I'd decided to use Mazda ac/p shortpath built the stage for it, but when I got the Mazda a.c. box out I had none.. there's about a dozen shortpaths but mostly ac/hl luckily I had 3 ac/p1s which only have a gain of 5.
Adjusted the bias resistor and set them up.
The only shortpath rectifier I had was a duffer, so its running on a cosser of the same era, but I have a few u12 mesh plates which I can try.
The cpu fans where rather noisy so a found a 6 volt power supply and ran them up.. perfect very quiet and they run cold.
The amp looks a mess on the board. But it's only for testing, if its good enough it will be built into a chassis
I have one lined up I made a few weeks ago.
It's been running for about an hour on my crappy office speakers. I'll check everything over and move it to the main speakers later.
It sounds pretty good so far. Very illuminated would my best description
20200518_200357_copy_768x1024.jpg
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
steve s
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#22 Re: Mofo

Post by steve s »

I didn't get it down stairs yesterday, had a couple of slight problems, the main one was I could hear a intermittent but slight crackling on one chanel after it had been running for a few hours., I could see it as a very low level intermittent dc voltage on the output
This mornings job is to find that.
I'll check all the simple things again before I start changing things, then I'll change the output caps and work backwards..
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
steve s
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#23 Re: Mofo

Post by steve s »

After a couple of hours running/ checking it over this morning the crackles have done a vanishing act

...so this afternoon i braved it on the main speakers..
The 1st 10 seconds gave a few more crackles as the directly heated rectifier kicked in, but then all went dead quiet. And its still that way 2 hours later..
Done that new amp frenzy, playing all the tracks that may upset it. None have .. in fact just the opposite.. I'm impressed.
There's a few improvements I need to do ( better output caps to start) but it easily beats anything else I've made so far . A bold statement I may take back in a few days.
I need to get rid of the circuit boards they are too big.+ not enough room for what I want to use. I can solder most of the components to the legs

The ac/p1s are doing a good job. May have another look in the garage at my rectifiers, could do to use indirectly heated.

If I cap couple, I could use any of my output valves to drive it, my interstages are only 25ma. So I'm limited in what I can use with them but at the signal voltages they are being used at, they are just about distortionless.
Just need a gain of around 5 or more giving me about same output as my px25 amp
I'm full of ideas..
I'll settle down with it, get used to the sound and then give it a few days before I leap onto changing it.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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pre65
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#24 Re: Mofo

Post by pre65 »

Well done Steve.

Looking forward to hearing (and seeing) the finished article. :)
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
Cressy Snr
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#25 Re: Mofo

Post by Cressy Snr »

Nice to hear it works and sounds fab.
Could be one hell of a good amp comparison at some point down the line. :lol:
Sgt. Baker started talkin’ with a Bullhorn in his hand.
steve s
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#26 Re: Mofo

Post by steve s »

Thanks for the comments gents
Its still playing can't turn it off. All's been well so far.
The cheap power supplys have been separated to keep them cool.
It takes about 10 minutes to warm up after I turned it off for couple of hours over teatime.
It is lovely and sweet. I've had a Suzanne Vega session for the last hour... result !!
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
steve s
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#27 Re: Mofo

Post by steve s »

Cressy Snr wrote: Tue May 19, 2020 5:33 pm Nice to hear it works and sounds fab.
Could be one hell of a good amp comparison at some point down the line. :lol:
Once the corona virus shits out the way, a comparison is on..
Last edited by steve s on Tue May 19, 2020 11:11 pm, edited 1 time in total.
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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IslandPink
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#28 Re: Mofo

Post by IslandPink »

That's very unfair on Chris :shock:
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pre65
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#29 Re: Mofo

Post by pre65 »

IslandPink wrote: Tue May 19, 2020 10:11 pm That's very unfair on Chris :shock:
Eh ?
The only thing necessary for the triumph of evil is for good men to do nothing.

Edmund Burke

G-Popz THE easy listening connoisseur. (Philip)
steve s
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#30 Re: Mofo

Post by steve s »

IslandPink wrote: Tue May 19, 2020 10:11 pm That's very unfair on Chris :shock:
Corona virus!...
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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