YMI5150 Early '68 12xxx build journal

[vanhalen5150]

Few examples of other amp builds. Caps are mixed, and totally opposite from tubes. Notice the one in which the guy sheilded every component lead. I would think that would have quite an effect on overall noise.
Some have said the line around the Sozo's is to denote the "foil" side of the cap. Is it, or is it just to help denote which way a cap is originally oriented in a chasis to a "preferred orientation" of a specific builder?

[YMI5150?]

wow, that shielded board is cool. I'm invisioning a large vat of parafin wax in a coffee can, drop the whole board in, ala Ed...

[vh junkie]

Any tone difference with carbon resistors? should I swap them out? Now's the time...

Not sure about the tone... but they will add more Schott noise (hiss!)

How about Sozo cap orientation? I see you were told to change orientation, George's build has orientation, but the instructions and another build I referenced did not. again, now's the time...

If you gonna change anything, you would do to two .68uf (but they look the hardest two change)... probably not worth the effort.

[YMI5150?]

more his with carbons or the ones I put on? if my layout has more inherent hiss, I'll swap them out tonight.

[vanhalen5150]

wow, that shielded board is cool. I'm invisioning a large vat of parafin wax in a coffee can, drop the whole board in, ala Ed...

With the heat generated from these amps I doubt any wax would be of any benefit. You would really need some good heat resistant insulation to do this job.

[vh junkie]

more his with carbons or the ones I put on? if my layout has more inherent hiss, I'll swap them out tonight.

Nah, yours are carbon film (quieter)... the NOS old school (squarer looking, darker ones)are carbon comp... more authentic but hissier...

wow, that shielded board is cool. I'm invisioning a large vat of parafin wax in a coffee can, drop the whole board in, ala Ed...

With the heat generated from these amps I doubt any wax would be of any benefit. You would really need some good heat resistant insulation to do this job.

Are you guys talking bout the stuff on the component leads? Looks like slip-on insulation sleaving to me...

[YMI5150?]

Fido says the carbon-comp resistors tend to break up a bit earlier so I may swap them out. not that hard to do...

[vanhalen5150]

more his with carbons or the ones I put on? if my layout has more inherent hiss, I'll swap them out tonight.

Nah, yours are carbon film (quieter)... the NOS old school (squarer looking, darker ones)are carbon comp... more authentic but hissier...

wow, that shielded board is cool. I'm invisioning a large vat of parafin wax in a coffee can, drop the whole board in, ala Ed...

With the heat generated from these amps I doubt any wax would be of any benefit. You would really need some good heat resistant insulation to do this job.

Are you guys talking bout the stuff on the component leads? Looks like slip-on insulation sleaving to me...

Yeh, its a clear white slip on. Not sure if its efective or not

[YMI5150?]

Update:
The basic build is complete. Please take a quick peak and see if there are any obvious errors. Fuses are in and its about ready to power up. I'm waiting for the missing board mounts to arrive (just arrived) and am going to build a quick stand for it. I should start verification tonight. should I grab a few slow blow fuses as backup?

The knobs are a tight fit and I tweaked the presence casing pushing one on. Appears to be functional but I'm going to replace it anyway. Thats why you see the two volume posts still bare. those two knobs needed a little reaming.

Lar/Mar kit on the way. Will install after basic build is up and running.

Parts also ordered to build a two stage attenuator - arriving Wednesday.

Busy week...

[vanhalen5150]

Fire it up!

[YMI5150?]

@ work for another hour. need to grab a 1x6 on the way home to stand it up a bit so I can see the tubes. reading the 82 page thread on the Lar Mar. falling asleep

hope my presence pot is functional enough to fire it up. will try to verify functionality beforehand.

stay tuned.

[vh junkie]

So your ready for static voltage tests? No tubes in for that. The voltages should read a bit higher thatn the chart.

Once the tubes are in you MUST have a speaker/load attached. Make sure the volumes are down, and retest the voltages.

[YMI5150?]

its alive! power is on. taking measurements now. no power tubes in yet. cabinet is plugged in now for safe measure. what a rush!

[YMI5150?]

need some help. all AC voltages measured well @ ~ 3.38v. switching to DC and measuring bias voltage I get 118v and no change when adjusting the pot. this is with standby position per George's directions. Nightowl's say to switch to high and measure but I want to verify that's okay to do first. PT bias voltage to board is 101vAC, says it should be around 90VAC.

hope to hear from you soon.

[YMI5150?]

here's a few shot. first documenting "time of birth" and the others are of the bias pot. I thought it might be suspect for high bias voltage but it appears correct. went ahead and powered up for a second and no change. reading is -121 VDC.