SP 12 SE

[laatsch55]

Tubes are a different animal for sure.

 

[laatsch55]

Thanks John, that helps a lot.

 

[speakerman1]

Hi Guys

Johnny can you explain why the pre tubes need to be matched more than the power tubes.

Lee I got a smile about the TT needing to be hooked up. Really I giggled about it. Maybe it is time grasshopper. The cart is set. You just need to set the weight. Set the weight to 1.5 grams.

I have to go and do more reading today. Did I send blacktops this time Lee? I will fix the sound barrier sometime in my life time. LOL

Larry

 

[laatsch55]

No these are clear Larrt. The tube swapout helped a lot. Just gotta get the phono se ction quieted down then I'll send her on. The old tubes were a definate part of the problem , heck I can give these new ones a good groping and no noise.

 

[speakerman1]

No these are clear Larrt. The tube swapout helped a lot. Just gotta get the phono se ction quieted down then I'll send her on. The old tubes were a definate part of the problem , heck I can give these new ones a good groping and no noise.

You going to try it out for awhile aren't you?

Larry

PS I'm in no hurry.

 

[laatsch55]

Oh yes, dead quiet now on everything but the phono section, man, they are sensitive. Good thging to learn though so it's all good. Actually had it on some sacrificials last night and sounded damn good.

 

[soundude]

Lee did the couplings help?
The reason for matching tubes in the pre stage is because the match effects gain. its very important to match all the resistors in those stages too, even the phono stage. If you gain is different between trodes by a factor of say 20, depending on the final output could increase the factor by 40 at the outputs..can be up to a volt difference at the speakers ..can check matches at the cathode resistors for voltage and see if they match. A transconductance tester is very important for this because it actually loads parameters of tubes like they are in the circuit and gives the overall gain and current properties. Dual triodes if they are old but nos are matched withing 5% for amplification factor from the factory...a hickok tester is the perfered test in these situations. Those tube you pulled out lee aren't bad they just have different style heater arrangment, the newer tubes have spiral heaters and cancel alot of hum like twisting the heater wires. those tubes have straight filaments and any stray ac can be picked up through the heater and absorbed by the cathode then amplified like the signal. I posted the Radiotrons Handbook that explains this and the filament would need to be biased higher than the cathode to reject the hum and noise. But that tube is the sweetest sounding 12au7 you will ever here....if you want to sell them I will take. Have put a few in my amps and when setup rite is a excellent performer.

 

[soundude]

heres the amp built for my son, the coolest thing is the brass is a door kick plate from Home craphole (DEPOT), and was cheaper than buying a chassis. but I have the clear top in this amp as the first gain stage, so its sound is just amplified all the way through...[attachment=1:2j78gy4l]IMG_4567.JPG[/attachment:2j78gy4l][attachment=0:2j78gy4l]IMG_4565.JPG[/attachment:2j78gy4l]

 

[speakerman1]

Also have a quad set of 12AU7As. ECC82 NOS. Will roll. You wouldn't believe what I paid for these tubes. I paid more for the ones Lee pulled than what I paid for both quads. LOL After I roll we can talk.

Larry

 

[speakerman1]

heres the amp built for my son, the coolest thing is the brass is a door kick plate from Home craphole (DEPOT), and was cheaper than buying a chassis. but I have the clear top in this amp as the first gain stage, so its sound is just amplified all the way through...[attachment=1:17iwuqa5]IMG_4567.JPG[/attachment:17iwuqa5][attachment=0:17iwuqa5]IMG_4565.JPG[/attachment:17iwuqa5]

Very Nice. Did you measure and bend? If so then you have a brake? I have some work I wanted to do. I don't have a brake or shear. I can or I use to be able to pull rivets that when painted there was no rivet. Flush cut the stem. Now you can use a Cherry Max the same as a D rivet.

Larry

 

[soundude]

Larry, there is no bends, built a wood frane and routered a recess so the plate was flush with the wood edge, brass screws secure it to the deck and hole sawed the controls and routered the holes.
but the whole front end of the amp is all med mu dual triodes...
When I build a system from scatch I like to have stages all seprate from each other, can concetrate on each stage and not worry about noises induced from phono or line stages.
I only like rivets when I use aluminum chassis and going to make enclosure on the amp..easy with rivets but if open looks better with shiny screws....I'm in the process of designing a EL34 amp, with 100w from 2 tubes but the potentials on the plates are 740vdc but the currents are low so the tube can live a decent life without the heat..front end is a pentode and phase splitter is triode..
Larry if you like tubes that much download the Radiotrons Designers Handbook, essential to tubes and loaded with information..I posted link in earlier tread, right off rutgers univesitys site. Think its RDH4 headfonz, google search.

 

[soundude]

Larry do you build, got a simple one for 6l6's or kt66's with a single tube on the front for gain and splitter, easy 45watts a channel, and awesome response.
some people don't like dealing with the high voltages so if you are one I understand...definitly hurts if you catch something while its on...OUCH!!

 

[speakerman1]

Larry do you build, got a simple one for 6l6's or kt66's with a single tube on the front for gain and splitter, easy 45watts a channel, and awesome response.
some people don't like dealing with the high voltages so if you are one I understand...definitly hurts if you catch something while its on...OUCH!!

I'm not scared of high voltage. I respect it a great deal though. There are certain things on aircraft that you disconnect and walk away for certain periods of time to dissipate. Igniter boxes and strobes. When a component pops when discharged it is good to leave it be for awhile.

I would like to build. My eyesight has gone on soldering small things. I may need new glasses. Just had an eye test though. That is why Lee is building the pre. I couldn't see to solder on the board.

Larry

 

[laatsch55]

Ok, so we are back at it. For skratch-=--the choke wires now have a good tight twist to em.
For Larrt-- the hi voltage wires were going under the board. I didn't think that was a good idea. So..... i took the 275 volt stuff and 120 and put em in the "Zippertubing" and routed it over the top.

 

[soundude]

Hi Lee, is the peamp quite? I noticed in the picture the nut that screws the board down touches the grounding trace. if you put back together and noisy, try removing the nut..

 

[Rex Everything]

Larry, there is no bends, built a wood frane and routered a recess so the plate was flush with the wood edge, brass screws secure it to the deck and hole sawed the controls and routered the holes.
but the whole front end of the amp is all med mu dual triodes...
When I build a system from scatch I like to have stages all seprate from each other, can concetrate on each stage and not worry about noises induced from phono or line stages.
I only like rivets when I use aluminum chassis and going to make enclosure on the amp..easy with rivets but if open looks better with shiny screws....I'm in the process of designing a EL34 amp, with 100w from 2 tubes but the potentials on the plates are 740vdc but the currents are low so the tube can live a decent life without the heat..front end is a pentode and phase splitter is triode..
Larry if you like tubes that much download the Radiotrons Designers Handbook, essential to tubes and loaded with information..I posted link in earlier tread, right off rutgers univesitys site. Think its RDH4 headfonz, google search.

How do you plan to get 100 watts from two EL34's?

 

[laatsch55]

Things are pretty settled down now EXCEPT for the phono section. Here are some observations

Input ---Left 10.32MV...............Right 10.32MV
Gain-----Left---all the way, Right---all the way
Volume------------1/2 way on both

Output-----Left 3.471 volts, Right 1.699 volts

Volume all the way up on both
Output-------Left 15.278 volts, Right 9.59 volts

Now if that's not weird enough,

Turn Left Input off,
Output-------Left 3.944 volts, Right 11.84 volts

Turn Right Input Off and left back on,
Output------Left 16.265 volts, Right 8.31 volts

Both inputs off, Left out 2.216 MV, Right out 6.4MV

WTF????????????????????????????

 

[laatsch55]

No 60HZ hum in any measurable quantity. The plastic that seals the shielding on my shielded cable was touching the signal wire. Peeled the plastic back further and a lot of garbage left.

 

[laatsch55]

By the way 275 volts DC bites like 480 AC. Harder to turn loose of also.

 

[laatsch55]

Hi Lee, is the peamp quite? I noticed in the picture the nut that screws the board down touches the grounding trace. if you put back together and noisy, try removing the nut..

The assembly instructions say to ground board to chassis.