ynor wrote: ↑Sat Feb 03, 2024 5:27 pm
Found it. But can't see OD trim of the AN ODR
Only the ones who have been inside the AN amp know for sure, but safe guess: 100k as in the original #60. That is what's in the layout indeed. The pic is of the original #60. I haven't seen any inside pic of AN's ODR.
But keep in mind, there is not just one ingredient that is decisive in the recipe. My #124 has low plates, a classic tone stack (for lack of a better term) and a 100k trimmer. Very Strat friendly amp.
The original #124 as it is now, has had updates: skyline tone stack and 345k trimmer (says 500k on the casing btw). #94 has a trimmer that says 1meg on the casing. I have a 1meg trimmer in my amp and it's the most gainy ODS clone I've ever heard. Much gainier than what I heard from the original amp in some clips from Gregor Hilden, so I doubt the trimmer is actually 1meg if you measure it.
Nevertheless, the trimmer is a great tweaking point and Dumble seemed to favour bigger trimmers for Strat players.
Looking at the layout: is there a 100k slope resistor in your amp too? That would account for some big bass in that amp too.
Yes there's a 100k slope resistor. It's not that the amp has too much bass actually. It's more a feeling and the way the amp responses to the touch of the strings. It feels somewhat flobby and uncontrolled on the strats, while with the LP and tele its thight and focused, where every nuance in touch is beautifully amplified. Hard to describe...
I hear you. I never really bonded with the skyline tone stack for that very reason. Great with tele's and humbuckers, but not what I like for a Strat. I found that I do like high plates with a Strat, but I also like my amps a bit darker with less sparkle than some others do.
But give the suggestions a try. Sub that 10n to the mid pot far a 47n. Different slope resistor. Changing plate and cathode resistors. Changing the trimmer. Not all at once, start with the simple ones and let us know what you hear and if it's in the right direction.
I'm putting together an order from Mouser for some mods on my JCM800 2205 soon. Can order parts for experimenting with the plate/cathode resistor, different tone stack and OD trim potmeter for the #102 modern eagle as well. Will I get caps and resistors of the same quality from Mouser that matches the components from Ceriatone? Or will I need to sorce them from somewhere else?
For experimenting with different parts I'd go to Tube Town in Germany. They have got 6PS caps at reasonable prices, they also have Vishay/Dale RN65 resistors. I think you can find there what you need. 6PS caps tend to be expensive at Mouser.
Thanks for that link man, haven't seen that before! Resolution is just good enough to see some details. First impression: nicely made but also efficient. Koa Speer resistors, IC caps on the cathodes. But most important: a low plate classic preamp!! That is much more like #124 (supposedly pre updates) than I would have thought. I can see all 1k5 cathode resistors in the preamp. No 180k on V1a. Also the filtering chain looks different than in #60.
I need to educate myself on resistors and caps! I live in Norway and have a package from Tube town waiting at the post office, but only new tolex for the ODS (smooth beige vinyl), filter caps and buffered fx loop for my JCM 2205.
Very exciting, what you're reading of that pic of the AN ODR! 1k5 on both V1A and V1B cathodes? 100k on both plates?
Indeed, 100k/1k5 on both triode halves of V1! Also definitely not a skyline tone stack. #60 definitely is a skyline tone stack. You can even read the pot values in some pictures: 250k, 250k and 500k (with 1n cap) in the original. But if the ODR is what you like, you'd probably like a #124 amp before the updates; a low plate classic.
If I'm interpreting this right, the AN ODR seems to be a hybrid between the early #124 low plate with classic tone stack and the reverb section of #60, while the #60 is somewhat of a "mid-plate" with Skyliner tone stack. So the AN ODR tone I'm chasing for my strats could be approximated by converting mine into #124 as I'm not interested in integrated reverb. I use a Quad Cortex in the FX loop for FX anyway, and will use it with the D-lator when that arrives next week.
I'm not that educated in these designs, but is it correct that it's not the plate resistor values that are of importance, but the actual voltage at the plates, which in turn is defined by B+ which may vary from different designs and transformers? So I should be chasing the correct plate voltages first by adjusting the plate resistors and then the ratio of plate/cathode resistors when converting into #124?
ynor wrote: ↑Sun Feb 04, 2024 10:32 am...is it correct that it's not the plate resistor values that are of importance, but the actual voltage at the plates, which in turn is defined by B+ which may vary from different designs and transformers?
"Incidentally, the terms high plate and low plate refer to the amount of voltage applied to the plates of the tubes, which can greatly affect any amp’s sound and playing feel."
But he was a bit confused or misled.
For a given supply voltage, the values of the plate (load) and cathode (bias) resistors (Ra and Rk) determine the static (no signal) operating point on the tube's characteristic of plate current (Ia) vs. plate-cathode voltage (Va-k) and grid voltage (Vg). Those two resistors (mainly Ra), also determine the path over which the point will move when signal is applied (the load line). Higher resistances decrease the slope of the load line and increase the stage voltage gain (Vout/Vin). Dumble seems to have used four specific combinations of Ra and Rk (100k & 1k5, 120k & 1k8, 150k & 2k2, and 220k & 3k3) in particular arrangements across the four preamp stages for the different amp types. The 220k/150k is called a "high plate," and 100k across all stages is a "low-plate."
ynor wrote: ↑Sun Feb 04, 2024 10:32 amSo I should be chasing the correct plate voltages first by adjusting the plate resistors and then the ratio of plate/cathode resistors when converting into #124?
No. Choose the plate and cathode resistor combinations, and then adjust the power supply dropping resistor just downstream of the choke to set the input stage plate voltage at around 200V or a bit less. The following dropping resistors remain constant to preserve the plate voltage relationships for the preamp tubes.
Here ya go. Change the resistors with the green values to what is in this modded layout and that is what gets you the low plate amp. Like Martin said: anodes should be around 200V for V1, 210V for V2. 180V on V1 still sounds good, just a bit different. I wouldn't fuss about it at this moment.
Changing values in blue should get you a bit closer to a classic tone stack, but...
Changing the pot values for treble, mid and bass and omitting the cap on the bass pot red values would complete that mod. Not changing the pots would only mean a different feel to the pots compared to a classic tone stack. They can still be adjusted to classic tone stack values.
Then there's the trigger pot that can be adjusted to taste. I think this is a 100k trimmer in AN's ODR, so maybe better left alone at this point.
Lastly the presence purple cap is 2.2uF now. In a #124, and probably also AN's ODR, this is 1uF. The presence control in your amp now affects a bit more (higher) mid range tan a 1uF cap would do. Can also be adjusted at a later point.
It's up to you where you start. Alle relatively simple mods, that can also be reversed. I've no clue how good you are with a soldering iron. For mods like these I always first take out the part I want to mod, then suck the solder out the eyelet, bend the new part to fit nicely, trim the legs and solder it in place. Make sure no wires drop out from the eyelet. The ones under the board are a pain to get back in.
Most importantly: work safe. Verify with a DMM that there is no high voltage left in the amp and the IEC cord is unplugged.
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Wow! Thank you all for your replies and for your time to help me chasing those last percents!
Don't know how I can repay you other than letting you know the results of your suggestions, and I sure will.
I'm not that experienced, but I do know how to handle a soldering iron and drain the caps before working inside the amp. Really appreciate the heads-up though
I just completed my High-plate classic rebuild and it's an absolute strat killer! I have a #0124 (low-plate skyline) and its not even close. I have a 3rd Gen (low-plate classic) and its pretty good with a strat but the HP classic has no real competition. You may want to leave your amp as a high-plate for now and do the "blue", "red" (leave the slope at 150K) and "purple" mods suggested by Rootz. The high-plate to low-plate is pretty simple and can be done later.
. I learned a lot I know about these amps on this board and am happy to pass that knowledge on again.
