[nikongod]

Quote:

Originally Posted by Ricey20 /img/forum/go_quote.gif Point to Point is not easy to troubleshoot when its very unorganized and all over the place. Not sure how organized most Supras are.

It didnt even take me an hour to draw up a schematic for BOTH amp section and psu for a P2P MPX3. There are wires going every which way, agreed, but they all go pretty directly to what they go to. FWIW, in all 3 of the SP toasters I have looked inside of, about 1/2 of the wires are there to hook something to the star-ground point. I suppose Mikhail could have used a ground bus, but there are lots of other compromises he could have made too.

There are only a few realistic topologies for an OTL tube amp. When you take the "only class-A" philosophy of SP you eliminate a couple which are capable of running class-AB and still sounding OK. Then the biggest thing separating the men from the boys is the power supply. A good power supply means a LOT to a tube amp (and many SS amps to a lesser degree too.)
Quote:

Originally Posted by Happy Camper /img/forum/go_quote.gif Go to a tv/radio repair that has a tube tech. With so many retired military, there should be tons of tube experience on the rock.

QFT.

If it is an issue of something rattling loose, it will be a simple visual check, and then repair.

 

[Akabeth]

What timing... Just wow. Hopefully someone can help me out

Last night I was listening to some Jazz tunes from my iPod. There I was leaning back after some reading assignments enjoying a well deserved break, eyes closed. All of a sudden about thirty minutes in, there was a 'screaming' hum from the right channel. I fell off my chair, tossed my R10 to the side and turned the amp off. I can't even remember the last time I had a panic attack.

I took out my Sylvanias output tubes, threw it in the garbage bin, replaced it with PFK's working tubes, the hum was noticeably lower, but still there. I've also rechecked it with a pair NOS RCA 6bl7gt's, the hum is also at a low level. thought for a minute it's a grounding issue because on minimum volume setting the hum (~60Hz tone) is audible; not enough to cause any sort of problems on rock tracks but DEFINITELY a problem for Classical, Vocal, Jazz based tracks where there's plenty of quiet passages. If it's any sort of indication: the hum gets louder when I turn the volume up. This is akin to putting my finger on the 1/8" tip of my 2.1 Logitech stereo's connector (makes that hum) and turning the volume up (hum gets louder).

Out of curiosity, I turned the amp on this afternoon just to hear my UX-3 which arrived today (what timing T_T). It sung well, but the hum was still there. My fear is I've 'somehow' melted a resistor, busted a power supply cap or something else in the circuitry. Any help will be appreciated.

Edit: I think I'll call Mikhail tomorrow.

 

[takezo]

it sounds like a powersupply filter cap went bad... just one side, correct?
the fact that the hum gets louder with increase in volume pot is
indicative that the issue is before the volume pot in the circuitry...
most probably one of the powersupply caps... it will get progressively
worse if you keep using the amp. i'd look for a qualified technician
in you area for help... or if waiting isn't an issue, send it in to mikhail.
good luck.

 

[Namrac]

I just agreed to purchase Aura's MPX3 Slam toaster.

I really cannot wait to get my hands on it.

 

[Gollie]

I have read this thread back and forth several times but I still have a few questions. Are the 6SN7W's the same are the Red Base 5692 and if so, is this considered a good output tube for the MPX3?

I have a SP MPX3 SLAM coming and i'm trying to get a few good tube options ready for when it arrives. I plan on using some of the 6SN7's (GTB's mostly) that I have already and I plan on getting some KEN RAD VT231's also. I would like to get some 5692's but not if they will be a waste on my new amp.

Thanks for the help!

 

[dee phazz]

I have exactly the same problem but for me that concerns the left channel, if you had a reply from Mikhail subject this hum could you please send me an mp. I 'm living in France and return my MPX3 for a long long time exclusively for that that 's frustrating !!!

 

[dee phazz]

Quote:

Originally Posted by Akabeth /img/forum/go_quote.gif What timing... Just wow. Hopefully someone can help me out Last night I was listening to some Jazz tunes from my iPod. There I was leaning back after some reading assignments enjoying a well deserved break, eyes closed. All of a sudden about thirty minutes in, there was a 'screaming' hum from the right channel. I fell off my chair, tossed my R10 to the side and turned the amp off. I can't even remember the last time I had a panic attack. I took out my Sylvanias output tubes, threw it in the garbage bin, replaced it with PFK's working tubes, the hum was noticeably lower, but still there. I've also rechecked it with a pair NOS RCA 6bl7gt's, the hum is also at a low level. thought for a minute it's a grounding issue because on minimum volume setting the hum (~60Hz tone) is audible; not enough to cause any sort of problems on rock tracks but DEFINITELY a problem for Classical, Vocal, Jazz based tracks where there's plenty of quiet passages. If it's any sort of indication: the hum gets louder when I turn the volume up. This is akin to putting my finger on the 1/8" tip of my 2.1 Logitech stereo's connector (makes that hum) and turning the volume up (hum gets louder). Out of curiosity, I turned the amp on this afternoon just to hear my UX-3 which arrived today (what timing T_T). It sung well, but the hum was still there. My fear is I've 'somehow' melted a resistor, busted a power supply cap or something else in the circuitry. Any help will be appreciated. Edit: I think I'll call Mikhail tomorrow.

I have exactly the same problem but for me that concerns the left channel, if you had a reply from Mikhail subject this hum could you please send me an mp. I 'm living in France and return my MPX3 for a long long time exclusively for that that 's frustrating !!!

 

[tagosaku]

Quote:

Originally Posted by Gollie /img/forum/go_quote.gif I have read this thread back and forth several times but I still have a few questions. Are the 6SN7W's the same are the Red Base 5692 and if so, is this considered a good output tube for the MPX3? I have a SP MPX3 SLAM coming and i'm trying to get a few good tube options ready for when it arrives. I plan on using some of the 6SN7's (GTB's mostly) that I have already and I plan on getting some KEN RAD VT231's also. I would like to get some 5692's but not if they will be a waste on my new amp. Thanks for the help!

You can use both 6sn7W (W, WGT, WGTA) and RB 5692 as output or driver. Right now, I am listening to RB5692 driving Syl WGTs, but don't think many likes RB5692 here.
In general I prefer GT to GTA/GTB, but there are so many possible combos and even more 'personal preferences'.

Good luck with receiving your MPX

 

[Frihed89]

I am with Tagosaku. But if you use the B's, remember you can use the high power option (higher plate voltage) with this tube and they do sound better. The Tung-Sols are dry and detailed. The Sylvania Silver tops are richer. The Raytheons are in-between.

But I would suggest you try to get some 6SN7GTs, and the best of these were made in WWII. For inputs, look at the 7062, 6414, 5965 (12AV7 family) and 12AY7 all with the same 9-pin adapter. There are many other adapters and tubes you can use.

And of course get two 5687 adapters that you can use with the 5687 and 7119 tubes as outputs, hence the Slam designation.

Enjoy!

 

[Skylab]

If you are willing to spend the $$$ you would have to in order to get a true 6SN7W (as opposed to a WGT), then you should really consider a ECC32 for the driver tube. This is really a great tube in the MPX3.

 

[tagosaku]

Quote:

Originally Posted by Skylab /img/forum/go_quote.gif If you are willing to spend the $$$ you would have to in order to get a true 6SN7W (as opposed to a WGT), then you should really consider a ECC32 for the driver tube. This is really a great tube in the MPX3.

True. And it is what Mikhail recommended last.

I happen to like Syl GT (short bottle) -> WGT -> W (short bottle) in general. Nothing wrong about expensive tubes. But there is always a possibility that you can enjoy not so expensive tubes also. Like GE GTB, TS GT (grey plate) etc. etc.
Also, eBay etc. sometimes have rebranded tube cheaper. Like NU GT listed as RCA GT etc.

 

[Skylab]

I totally agree - the Sylvania short-bottle 6SN7WGT is a great sounding tube, and can be had relatively cheap.

 

[Jahvetti]

X2 for Mullard ECC32, if the transformer can give the heater current.

 

[Skylab]

Quote:

Originally Posted by Jahvetti /img/forum/go_quote.gif X2 for Mullard ECC32, if the transformer can give the heater current.

This is no problem for the SP amps

 

[mrarroyo]

Anyone using a 6BL7GT as a driver?

I understand they can be used as an output tube, right?