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Re: 68 plexi
Posted: Mon Jul 04, 2016 3:55 pm
by Tazin
The amp referred to in this thread is wired up correctly.
Re: 68 plexi
Posted: Mon Jul 04, 2016 4:39 pm
by whopperplate
Thank you Tazin.
Does the writing change how the filter caps react? Wouldn't the cap see more voltage in this orientation? I imagine this would be harder on the cap and could at least add noise.
Charlie
Re: 68 plexi
Posted: Mon Jul 04, 2016 6:26 pm
by Tazin
If you look at a schematic for this earlier style preamp filter cap layout you'll see it functions the same as the later style with the preamp filter cap mounted either topside or the '69 style with the cap mounted internally near the PT.
Re: 68 plexi
Posted: Mon Jul 04, 2016 9:48 pm
by RockinRocket
Regardless of value CC absorb moisture over time and drift well out of spec. I probably wouldn't waist money on expensive AB CC since you don't really know where they were stored. What if the 8k2s measured 16k each? Brown sound Im sure could help
Re: 68 plexi
Posted: Tue Jul 05, 2016 7:46 am
by whopperplate
Oh I have ' wasted' plenty of money on valve storms and George's NOS AB resistor stash; they test in spec, I trust them
whether 8k2 or 16k4, i will trust my ear to decide if the 'stock' value will suffice and add resistance where necessary. again, I was initially referring to the 10k Iskra 1watt Carbon film not the CC 8k2, but definitely interesting points to consider.
Charlie
Re: 68 plexi
Posted: Tue Jul 05, 2016 8:38 am
by RockinRocket
Yep my post was directed at why the amp was so brown. If the 10ks wernt wired correct the amp would have more volts. More volts isn't what would cause this amp to sound so brown. However the CC 8k2 drifting way out of spec could be one reason or the reason.
Re: 68 plexi
Posted: Tue Jul 05, 2016 12:40 pm
by whopperplate
True, but I think only if those 8k2 drifted WAY out of spec, as higher value R values here are more regularly common than super brown tones such as this. In my experience dual 10k seems to take way too much clarity in a low filtered circuit such as this. I am thinking, other than the OT as already mentioned, the tone stack may have more to do with the character goin on here i.e. Over spec midrange pot
seriously though the fatness of the midrange is clear even from listening through crappy little iPad speakers.
My replica, more or less, is currently almost ready to start populating the board. Hopefully in a week or two I will be posting some pics and sound samples to further this conversation.
Charlie
Re: 68 plexi
Posted: Tue Jul 05, 2016 3:58 pm
by RockinRocket
Maybe but that amp sounds like it has low volts. If it was a salvation army amp who knows wheres it was stored if it ended up at a thrift store. My guess it was sitting in someones garage, attic or who knows where before if finally got moved ya know? Its just strange. Sitting out in the garage im sure it picked up all kinds of moisture
Re: 68 plexi
Posted: Fri Jul 08, 2016 10:18 pm
by whopperplate
So I notice the v1 grid wires are ran up into the perf board very close to the plate resistors in this amp. It would seem the way the bright channel grid wire runs it bumps up right against the turret for the plate resistor under the board, unless it's got some extra slack. Looks stock as well. Probably induces some extra noise, no?
Charlie
Re: 68 plexi
Posted: Wed Jul 06, 2022 2:25 pm
by uiovbged332