Steel String Singer #005 build

[rccolgan]

Sooooo clean!! What an example build!

[captaincoconut]

Thanks, Ryan! Let's hope it sounds as good as it looks

Curiosity got the better of me, so I powered the unit up yesterday without any tubes plugged in. No blown fuses so far! Yay!

[rccolgan]

Thanks, Ryan! Let's hope it sounds as good as it looks

Curiosity got the better of me, so I powered the unit up yesterday without any tubes plugged in. No blown fuses so far! Yay!

lol I'm 99% sure with your attention to detail, you got this! The only uncertainty would be the OT primaries "correct" which is always a 50% chance. (altho I feel like I'm 90% wrong every time lol)

Looking forward to your review!

[captaincoconut]

Okay, so I did a first test run today with only the preamp tubes installed. It powers up fine, no smoke coming out yet. However, some of the voltages I measured seem...way too high? Even when taking into account that the load of the power tubes is missing, some of that doesn't look right.

Power transformer is the same as in the schematic, output transformer is a Hammond 1760W (not sure what exact transformer @beasley used in his build).

Nominal wall voltage here is 230VAC, actual wall voltage today was 232VAC. I used the exact same dropping resistor chain as found in the schematic, except for the FET booster where I used 150k/8.2k instead of 56k/8.2k. Sections that are crossed out are missing in my build or were done the traditional Dumble way (passive effects loop, traditional FET boost)

Opinions? The voltages I measured are in red, @beasley's measurements in blue.

[martin manning]

I would put the power tubes in and see if you can bias them. I’m not sure why people tend to start with the preamp tubes. I’m betting the voltages will come down.

[captaincoconut]

Too bad the power tubes are still on the way to me

[Guy77]

Too bad the power tubes are still on the way to me

Hammonds tend to be conservatively rated on their secondary voltages so the 325-0-325 may get you a little higher than expected and with your wall voltages over 230VAC the voltages numbers you are getting actually look correct.

I am betting you come down to the 450 - 460v plate voltage range with power tubes installed.

Cheers
Guy

[captaincoconut]

Cool! I was/am just concerned because some of the anode voltages are much higher than what Beasley had in his build. Look at the reverb recovery stage and the reverb mixer - that's almost 90V above what he measured.

I'm just lacking the experience with what to see as normal/unconcerning behavior as all the amps I had built so far were very straight forward builds and not near as complex as a SSS. So pardon me for being a bit anxious, please

[captaincoconut]

The only uncertainty would be the OT primaries "correct" which is always a 50% chance. (altho I feel like I'm 90% wrong every time lol)

Joke's on you, the OT was indeed wired the wrong way around. I almost fell off my chair when I flipped off the standby switch

Okay Gentlemen, here's where I am at: I put in some JJ 6L6GC tubes. I have sound! Every potentiometer, every toggle switch, every relay works as intended. Reverb works fine. Yippie!

The amp seems to be free of excessive noise - at least there's no hum or anything else that you wouldn't contribute to having the chassis sit openly on my table.

Regarding voltages:
1. Plate voltage drops to 445V with power tubes.
2. Bias voltage range seems to be a bit problematic. Lowest I can get is 47mV/47mA. Which is fine at that specific plate voltage:



However, I would like to lower the available bias range, should I ever need it. My first instinct would be to raise the 56k resistor entering the balance potentiometer?



3. With the power tubes in, all other voltages (see measurements in one of my previous posts from this week) dropped around 20V. Not sure how to feel about this? Is this something I want to change, i.e. try to lower the voltages even more, trying to get them closer to what @beasley measured in his build? I will make another thorough voltage measurement for each single spot when I find the time.

4. The FET boost voltage is dropping down to 13.5V. Should I just play around with the voltage divider values to get this down to 9V or bias the FET to half/third of 13.5V?


Here's a really short video demonstrating that the amp is - actually - working, it's not a sound demo Sorry for butchering all the cliché licks. The slight distortion is coming from having the FET boost and preamp wide open.



Cheers!

[rccolgan]

LOL I hate it when that happens!!

Congrats!! You unofficially have won Amp Garage Member of The Day with this build! Enjoy!

[captaincoconut]

LOL I hate it when that happens!!

Congrats!! You unofficially have won Amp Garage Member of The Day with this build! Enjoy!

Thanks, but I'm not finished yet!

[martin manning]

I am hearing some good tones in there!

Does the distortion only occur when the FET is switched on?
What are the voltages at the top and bottom of the drain resistor now?

You could go either way if you want to adjust the bias. That 13V will be strongly affected by the bias point, a little hotter bias will bring that down.

For the bias voltage range, I would reduce the 56k feeding the balance pot.

[captaincoconut]

I am hearing some good tones in there!

This was with the master volume on 0.00001 because I didn't dare to go higher yet. But the tone is there for sure!

Does the distortion only occur when the FET is switched on?

No, there is some slight distortion happening when I crank the preamp volume.

What are the voltages at the top and bottom of the drain resistor now?

I measured 13.5V Vdd and set the bias trimmer so that I had around half of that across the drain resistor. Initially it was lower (as intended, 1/3 of Vdd). Will play around with it a little.

You could go either way if you want to adjust the bias. That 13V will be strongly affected by the bias point, a little hotter bias will bring that down.

Good to know!

For the bias voltage range, I would reduce the 56k feeding the balance pot.

Ok, will try that.

[captaincoconut]

Nothing super exciting, but I wired up this footswitch for the amp today. It's a 1590DD sized enclosure that I had drilled, powdercoated and UV printed at Tayda Electronics. Came out really clean, love their printing service.

[dbharris]

Looks very professional!

-Dan