50w seems louder than 100w

[pdf64]

I recall that CTS audio taper nominal is 10%, whereas Alpha is 15%. It would be best to verify that on the manufacturer’s website.
Mention has been made of a 20% tolerance. That is typically regarding the total track resistance, not the taper’s conformance to nominal. As per my previous post, a pot’s conformance to its taper nominal is generally untoleranced, eg ‘that’s what we’re aiming for, but we can’t guarantee where it will end up’.

[talbany]

The older CTS's Fender used were the 2-35 The 35 is the taper designation meaning if you set the wiper at 1/2 trace gives you 35% of the total value..a "linear" taper would of course be 50%. So the higher the taper the more linear the pot reacts and the more linear the pot reacts the quicker the volume comes up on you..This is why an old Fender set at 3 is fairly loud. So why did Fender do this?..Easy made their amps seem like they were louder and what happens when you get past 6?..Not much (CTS also made a J taper which was 30% work great in these amps)

So there are 2 things to measure in a pot..Total resistance and the resistance with the wiper set at the 1/2 way portion of the trace and determine the taper.
Both newer CTS's and the Alphas tapers are all over the place unless you order directly from them and specify your taper
I mean seriously how many people out there check the taper when there pots arrive and do you think Nik checks them
Tony

[philbard]

The older CTS's Fender used were the 2-35 The 35 is the taper designation meaning if you set the wiper at 1/2 trace gives you 35% of the total value..a "linear" taper would of course be 50%. So the higher the taper the more linear the pot reacts and the more linear the pot reacts the quicker the volume comes up on you..This is why an old Fender set at 3 is fairly loud. So why did Fender do this?..Easy made their amps seem like they were louder and what happens when you get past 6?..Not much (CTS also made a J taper which was 30% work great in these amps)

So there are 2 things to measure in a pot..Total resistance and the resistance with the wiper set at the 1/2 way portion of the trace and determine the taper.
Both newer CTS's and the Alphas tapers are all over the place unless you order directly from them and specify your taper
I mean seriously how many people out there check the taper when there pots arrive and do you think Nik checks them
Tony

That's really good information. From what I can discern of the measurements, the 2 Alpha's come up faster than the 2 CTS's. The CTS's are 2033's, FWIW, and measure 100K at 1/2 trace (1M pot). Thats pretty slow, but actually for an amp this powerful is fine for me.

[norburybrook]

The older CTS's Fender used were the 2-35 The 35 is the taper designation meaning if you set the wiper at 1/2 trace gives you 35% of the total value..a "linear" taper would of course be 50%. So the higher the taper the more linear the pot reacts and the more linear the pot reacts the quicker the volume comes up on you..This is why an old Fender set at 3 is fairly loud. So why did Fender do this?..Easy made their amps seem like they were louder and what happens when you get past 6?..Not much (CTS also made a J taper which was 30% work great in these amps)

So there are 2 things to measure in a pot..Total resistance and the resistance with the wiper set at the 1/2 way portion of the trace and determine the taper.
Both newer CTS's and the Alphas tapers are all over the place unless you order directly from them and specify your taper
I mean seriously how many people out there check the taper when there pots arrive and do you think Nik checks them
Tony

another reason to replace the fender reverb pot with a linear one too

M

[pdf64]

I hate modern CTS pots, 15% of their rotation is wasted on a dead zone at the start, presumably to accommodate use with (rotationally) switched pots.
If a 10% taper is desired, Bournes are my default choice.

[Audiodog]

250ish is way too much voltage on the preamp tubes. Knock it down to 200-210. Should sound a lot better.

Is there a FET? If not, that explains the high voltage. Hang a resistor to ground off the last node and that simulates the load and brings things into spec. I have used 150k to 220k depending on the situation.

Hey All,

So I’ve just finished my first 102 build from scratch, a 100w model. Comparing it to the CTone OTS 50w I finished in December, which was my first build, the 50w is louder. This with all pot settings matched, identical tubes in all the positions and using the same speaker. I know some folks have said there isn’t as big a difference between the two as the numbers 100 and 50 would suggest, but I’d still expect the 100w to be a more powerful amp. They both sound great, and very close tonally, I’m not unhappy at all but curious. I’m wondering if I don’t have something quite right.

Both amps are biased to around 55%. The CTone uses their proprietary transformers, I’ve got Magnetic Components in the 100w. Ceriatone’s PT output is 690v and the Magnetic Components is 640v, but plate voltages are similar on the power tubes, in the 440 to 450v range. Preamp tube plates are 250ish on the 100w and 200ish on the 50w, both amp’s PI plates are around 290v. I’ve got the same pots in all positions, so taper is not involved, since I’m home I don’t crank it beyond moderate volumes. With the Volume at 4 on both amps, the loudness matches when the Master Volume settings on the 100w is at 3 and on the 50w at 2. So the 50w actually seems more powerful. Both amps behave the same when OD is on.

I’ve rolled the tubes and all are working fine. Looking at the schematics there are a few differences in components beyond the trannies and the number of power tubes. Here is what I see….

V1A grid stopper: 50w 22K, 100w 33K (Jumpered a 68K in parallel to the 33K on the 100 and it made no difference in volume)
PI plates: 50w 110K and 100K, 100w 120K and 110K.
6L6 Screens: 50w 1K, 100w 470R
6L6 grid stopper: 50w 3.3K, 100w 5.1K

I’ve done a little poking around with an oscilloscope inputing a 1v RMS 100Hz signal, preamp seems to be working OK, but with the scope I have I can’t read very high signal voltages so don’t know what they are off the PI into the power section. I suppose its conceivable only half the power tubes are actually amplifying signals, but all connections seem solid. Any suggestions on how to determine if there are problems in the power section are welcome.

What am I missing here, if anything?

[philbard]

250ish is way too much voltage on the preamp tubes. Knock it down to 200-210. Should sound a lot better.

Is there a FET? If not, that explains the high voltage. Hang a resistor to ground off the last node and that simulates the load and brings things into spec. I have used 150k to 220k depending on the situation.

Yeah I thought that too shortly after starting this thread and did some poking around. I discovered what the problem was. I'm using the classic power supply and I had a 2.2K resistor between B+3 and B+4 instead of the 22K that was required. Swapped it out and both voltages dropped to around 200 right away.

Thanks for the info. Cheers.

[Audiodog]

How does it sound? Better?

250ish is way too much voltage on the preamp tubes. Knock it down to 200-210. Should sound a lot better.

Is there a FET? If not, that explains the high voltage. Hang a resistor to ground off the last node and that simulates the load and brings things into spec. I have used 150k to 220k depending on the situation.

Yeah I thought that too shortly after starting this thread and did some poking around. I discovered what the problem was. I'm using the classic power supply and I had a 2.2K resistor between B+3 and B+4 instead of the 22K that was required. Swapped it out and both voltages dropped to around 200 right away.

Thanks for the info. Cheers.

[philbard]

How does it sound? Better?

I think so, I didn't so much check for a difference immediately after swapping the resistor though, probably should have thought to do it right away. But I notice that it has developed a really beautiful tonal quality and gets better every time I play through it. Its my favorite amp against a Mesa, Fender Custom Deluxe and my first build, the Ceriatone 50w.

Here's a clip of Portland Blues master Robbie Laws performing with it the other night... overdrive turned on at the halfway point.

https://www.youtube.com/watch?v=oIXr_unp340