Bringing Up My First Amp

[norburybrook]

the original was biased at 30.3 mA from a plate voltage 465vDC


you can work backwards to work out what percentage that was.

I'm now in Australia and my brain is still addled so I'll leave it to someone else...……...




MC

[talbany]

It says it right on the layout 30.3 taken right off 183 at the time the amp was examined and partially blue printed. 37.6 mA would be 70% (normal) so yes he ran them slightly colder. IMO I like to run my 34's hotter around 65% try both it really depends on what sounds and feels best to you!
https://ampgarage.com/forum/download/fi ... &mode=view

Tony

[donvan]

It says it right on the layout 30.3 taken right off 183 at the time the amp was examined and partially blue printed. 37.6 mA would be 70% (normal) so yes he ran them slightly colder. IMO I like to run my 34's hotter around 65% try both it really depends on what sounds and feels best to you!

Tony

Thanks for the response Tony. It's helpful to know what bias percentage others prefer. I had seen the bias notes on the 183 layout earlier but I also saw that the layouts for 183 and 102 BOTH said that the bias was 30.3mA @ 465.5V. I didn't think both would have the same exact numbers to that precision on two different power amp circuits so I assumed that one of these was a guess or that there was a copy and paste error.

Thanks,
Don

[talbany]

Don
Like I said in my previous post.
Looking back over my notes I did find where Shad (Quinn amps) sent me the mail regarding the bias setting on 183. As he was the one who blueprinted the amp and made an exact replica for the owner at the time he was in the amp. IIRC the tubes in 183 at the time were the older Siemens/RFT EL-34's
The 102 info was collected through several sources who had been inside the amp but unfortunately did not give me the exact bias settings AFAIR I could, of course, be wrong and my memory has failed me in the past as this was a long time ago . The only thing that comes to mind is either A. 102 had a plate voltage of 465 and therefore I assumed the bias (dissipation @ idle) was what Dumble was using at the time or put it there as an example as to what percentage Dumble was using to set his output tubes. Either way?. You lucked out and the 183 bias voltages written on the layout was what 183 was running at the time the Layout was done.

Again Personally I think this is a parameter people get carried away with wanting to set the bias exactly the way Dumble did!. IMO this is a personal setting (like a presence control)I generally recommend with your particular style, set of output tubes/guitar/speaker cab, starting at 70%. Play the amp roll it back 5Ma, play the amp and repeat until you find the setting you prefer is IMO setting the amp to respond to your needs not Dumbles. I would be more concerned with things i cannot adjust

Jazzers like em cold. Rock guys like em hot and the grunge guys are just glad to see em work it's a Joke!

Tony

[donvan]

Tony,
Once again, thanks for taking the time to respond to someone who has only built one amp. Your experience is invaluable.

Don

[donvan]

Silver Mica capacitors were discussed in another thread and this got me looking closer at the capacitors in my amp. I don't have any silver mica caps but one cap that I am using looks "suspicious" to me. I actually don't remember why I selected it. Perhaps it came from someone else's BOM. Anyway it is the 390 pF treble cap. It is a TDK and is called a high voltage safety disc capacitor. Looks like it's designed for automotive applications not audio.

Does anyone have any experience with this type of capacitor?


https://www.mouser.com/new/tdk/tdk-high ... apacitors/

[Abe5150]

I used the other ceramic automotive ones and they worked fine. They were called Murata high voltage high temp ceramic.

[Tony Bones]

If it bothers you then get some different caps and try them. If you prefer one over the others, then you've learned something. If you can't tell the difference, then you've learned something.

[donvan]

If it bothers you then get some different caps and try them. If you prefer one over the others, then you've learned something. If you can't tell the difference, then you've learned something.

I didn't say it was bothering me or that I don't know what I should do. The question was, does anyone have experience with this seemly odd type of capacitor - a "high voltage safety cap".

[donvan]

A long time ago I had posted a little clip of how I dialed a Strat (middle + bridge combo) on a 102 amp, I found it here on the board and am attaching it again. It was recorded far form the speaker cab an not pointing at it, so it sounds darker than it actually was in the room. At the end of the day, for a Strat, my favorite voicing was the "classic" and I had added some tweaks at the OD entrance to smooth out the sound even more.

Gil,
I read through some of your old posts on getting a good OD tone with your strat. At the time, you said you didn't like the tone you got from noiseless pickups but that you did have good results with 57/62 pickups.
When you switched to 57/62 pickups did you also change the guitar pots and cap?

The reason I ask is because My American Deluxe from 2000 came with 1 meg pots, a . 022uF tone cap and noiseless pickups. It also came with an r/c treble bleed prevention circuit.
I would think that it would make sense when switching to vintage style pickups to also change the components to vintage values - 250K pots, and .1uF cap.

Did you do that or did you just swap out your pickups?

Thanks,
Don

[ayan]

In my case, they were different guitars. The Noiseless were in a Clapton Strat, and for a long time I replaced the pickguard (getting rid of the active stuff) with another one loaded with Kinmans, 250K pots and .1uF tone cap. Eventually I returned it to stock and sold it. The other guitar is a 62 HR, which I still have. Stock with 57/62 pickups and 250K pots, I replaced the .047uF cap with a .1uF one. I installed a treble bleed on that as well, forget the values, but it's nothing too radical.

A long time ago I had posted a little clip of how I dialed a Strat (middle + bridge combo) on a 102 amp, I found it here on the board and am attaching it again. It was recorded far form the speaker cab an not pointing at it, so it sounds darker than it actually was in the room. At the end of the day, for a Strat, my favorite voicing was the "classic" and I had added some tweaks at the OD entrance to smooth out the sound even more.

Gil,
I read through some of your old posts on getting a good OD tone with your strat. At the time, you said you didn't like the tone you got from noiseless pickups but that you did have good results with 57/62 pickups.
When you switched to 57/62 pickups did you also change the guitar pots and cap?

The reason I ask is because My American Deluxe from 2000 came with 1 meg pots, a . 022uF tone cap and noiseless pickups. It also came with an r/c treble bleed prevention circuit.
I would think that it would make sense when switching to vintage style pickups to also change the components to vintage values - 250K pots, and .1uF cap.

Did you do that or did you just swap out your pickups?

Thanks,
Don

[donvan]

Thanks Gil,
That makes perfect sense.