SKYLINER build - inspired by ODS #124 and #060

[martin manning]

Early impressions... It's very quiet (hiss) dead quiet really, unless I stand too close to it with the guitar. A quick run through of the various switches, FET, PAB and OD - all work as expected. Tone controls and EQ switches are all ok. The presence isn't noticable but the tubes haven't been biased yet and I will look into what factors will bring it into play...

Congrats, you deserve a celebratory drink!

BTW, if the NFB loop is open you won't have any presence control ;^)

[ijedouglas]

I've left it there for tonight and hit the bottle in celebration. Many questions answered today, the least of which being was it worth it?

I would say so.

Congrats and enjoy!

[bepone]

I've left it there for tonight and hit the bottle in celebration. Many questions answered today, the least of which being was it worth it?

no need a reason for that at all but is ok consgratulations! soon we will hear the sound

[Stephen1966]

Early impressions... It's very quiet (hiss) dead quiet really, unless I stand too close to it with the guitar. A quick run through of the various switches, FET, PAB and OD - all work as expected. Tone controls and EQ switches are all ok. The presence isn't noticable but the tubes haven't been biased yet and I will look into what factors will bring it into play...

Congrats, you deserve a celebratory drink!

BTW, if the NFB loop is open you won't have any presence control ;^)

Doh!

[Stephen1966]

Reconnected the NFB and [holding breath] switched it on = silence. All good.

Presence control now has some effect. It's running at about 42% Pd at the moment, so hardly glorious but given the different biasing methods out there. Do you have a favourite?

Addendum: which is to ask, are there any quirks or peculiarities about biasing the ODS quad you have insight on?

[martin manning]

The consensus seems to be generally on the cool side, around 55-60% Pa max based on cathode current.

[Stephen1966]

The consensus seems to be generally on the cool side, around 55-60% Pa max based on cathode current.

Thanks, I'll give it a go. The OD has plenty of grunt even at this very cool setting. I'm not looking for a metal "chug". That's for players with a high metabolic rate - not me I'm also going to be pairing it with an EVM 12L so I'm expecting a pretty tight OD lead tone with some punch. Key will be getting the PI trim right, I suspect.

[bepone]

ok no oscilations, you can do anything with the amp now. recheck all the voltages, anode cathode, V1, V2.. and you can approach to the tone questions after first start to see where you are

1. clean tone: bass quality=? flabby/soft/too much/muddy/stiff? (the best - stiff bass on clean, difficult to get)
2. clean tone middles=? sweet/irritant/thick/thin/enough/not enough? (the best - thick mids+sweet)
3. clean tones highs=? again thick/thin/sparking/smooth/dull/irritant/unpleasant/sweet?

4. Rock OD without boost =? farting/unbalanced/harsh/too bassy/sounding like crap/smooth/excellent/fizzy/fuzzy/thin/good sustain?
5. Rock OD with the boost . like above but is better, should be ok because bass if filtering out with the treble cap (its high pass filter with the vol pot), tone controls are off and this is the best tone to me

6. Jazz OD - lower gain but increased should be very good and balanced
7 .Jazz OD with the boost ON + slide on guitar should be excellent

i forgot something for sure but this is for the start

[Stephen1966]

Thank you, bepone. This is quite detailed and will help me to think about it at a more granular level. Even without any biasing I've hit on some sweet tones so once I start to get the headroom and bias the PI I'm hopeful it will be a winner.

Because the PSU is unique to this amp, I spent a bit of time yesterday measuring and quantifying the differences between what I know to be good (the published voltages in the 1.6 schematic), the simulation which included the reverb, and the actual voltages measured over a couple of days. My voltages are all within about 5% of the original so I think I am happy with that. These will change again when I start the biasing but I think I can put that part of the process to bed, make the solder connections on the PSU more permanent (the soldering was done very lightly in case I had to replace any components) and a general once-over checking for any more bits of debris before I flip it over and start on the biasing. I can't get a good look at the tubes the way it is rigged up at the moment. I'm familiar with red-plating but it will be better this time.

Then its all a bit subjective regarding tone until I have the speaker paired up but I am seeing real shortages of plywood stock to build the cab. Wood and metal supplies seem to have been hard hit by the pandemic. I don't really know why.

I should be making some progress shortly, so stay tuned

[bepone]

ok what cabinet are you building? 2x12"? 1x12"? if the last, 1x12", i can recommend as big as possible, oversized, 19mm pine board x 250mm x 1-2m from Bauhaus! and for the front baffle birch ply of 12mm thickness! easy to find in Bauhaus, they will also cut there for free'

[Stephen1966]

ok what cabinet are you building? 2x12"? 1x12"? if the last, 1x12", i can recommend as big as possible, oversized, 19mm pine board x 250mm x 1-2m from Bauhaus! and for the front baffle birch ply of 12mm thickness! easy to find in Bauhaus, they will also cut there for free'

It will be a 1x12 but 24" (to match the head) x 18" x 12". The top, bottom and sides are going to be pine but I just don't have enough 12mm birch ply for the back of the cab and the head. The pine boards have been sitting under my bench for months, experience with these is that once they really dry out, the knots can come lose and just fall out. Pine may be a good local timber and has a nice resonance but it is almost impossible to find knot-free in any length so can't remember how much I have, it's a lot, and I'll cut those for the best pieces.

Bauhaus https://www.bauhaus.cz/preklizka-multiplex-22390495 Super! Never thought of them. I'll drive up there later this week and pick it up if it's still in stock. Pankrac, is about an hour away in Prague. Bugger to drive around but it gives me an excuse to get out of the house.

[bepone]

you can return the knots back, with a little bit of glue! after is tolex and forget it..

i think front baffle cut will cost you peanuts..no need to take complete board of ply, only small piece they will do.. cca 10 Eur, they usually have the big saw in the back of the store, just ask.. for one small piece of baffle they dont charge anything, or maybe 1-2 Eur for cutting, 2 min of job. and you save 2 h of preparation, and lousy cutting at home, and cleaning after

[Stephen1966]

you can return the knots back, with a little bit of glue! after is tolex and forget it..

i think front baffle cut will cost you peanuts..no need to take complete board of ply, only small piece they will do.. cca 10 Eur, they usually have the big saw in the back of the store, just ask.. for one small piece of baffle they dont charge anything, or maybe 1-2 Eur for cutting, 2 min of job. and you save 2 h of preparation, and lousy cutting at home, and cleaning after

5 minute epoxy is perfect for that. After all the doors, stairs, kitchens, pergolas and terraces I've built, I have a pretty well tooled up workshop the kids even buy gift cards for OBI - my hardware store - for Christmas and birthdays. They know me too well, I think! So, I have my own big saw The cutting service is good if it's available and for anyone less well provisioned you will get good results for little if any extra cost. I think all the big hardware stores around here and back in the UK will do it, I'm sure there will be similar services in the States. If you want to do things like finger joints like in Fender cabs or dovetails as I do, you really need to do it yourself. I know what you're saying, I started with a hammer and ended up with a workshop. When you're inbetween and you haven't spent the thousands on tools, it's best to farm it out.

[Stephen1966]

The consensus seems to be generally on the cool side, around 55-60% Pa max based on cathode current.

When you bias this way, do you measure and subtract the screen current? I'm assuming it might only be as much as 5% of the cathode current total.

[martin manning]

The consensus seems to be generally on the cool side, around 55-60% Pa max based on cathode current.

When you bias this way, do you measure and subtract the screen current? I'm assuming it might only be as much as 5% of the cathode current total.

Strictly speaking yes you should subtract screen current to calculate actual anode dissipation, but most people just calculate it using cathode current. Screen resistor voltage drop is an easy way to get the screen current.