Mike Clayton wrote:That's the one, thanks. I prefer bias wiggle trem like on Princeton, do you know why they went to the optocoupler?
I can’t say for certain, but it might’ve been that the optocoupler design was the best way (they could think of) to have tremolo on only one of two channels. It’s also more consistent in its effect, whereas the strength of bias-wiggle trem can vary with the bias point and age of the output valves. From a design perspective, messing with bias is not a good idea since it does put extra strain on the output valves. I’ve seen a few Holden amps that’ll start to redplate if you crank the tremolo intensity, for example.
This is all supposition though- most people would just say Leo made all his decisions based on miniscule cost savings!
Mike Clayton wrote:That's the one, thanks. I prefer bias wiggle trem like on Princeton, do you know why they went to the optocoupler?
I can’t say for certain, but it might’ve been that the optocoupler design was the best way (they could think of) to have tremolo on only one of two channels. It’s also more consistent in its effect, whereas the strength of bias-wiggle trem can vary with the bias point and age of the output valves. From a design perspective, messing with bias is not a good idea since it does put extra strain on the output valves. I’ve seen a few Holden amps that’ll start to redplate if you crank the tremolo intensity, for example.
This is all supposition though- most people would just say Leo made all his decisions based on miniscule cost savings!
I think your last sentence is the most likely reason!!
Cdog wrote:I put a cap across my roach too.... Used a 27n as that's what I had at the time. It smooths the waveform a little, but still sounds good.
Interesting, that's twice+ the value of the recommended cap (.01 uF). It must be effecting the neon's pulsing waveform - did you see the tremolo waveform change on an oscilloscope?
Feeling pretty satisfied because I've just completed the '64 Vibroverb amp chassis that I've been building for the last 5 weeks The .01uF cap across the roach's neon to ground fixed the tremolo ticking. She's all biased up (at just under 70% max plate dissipation which is 21 Watts for my TAD 6L6GC's) and sounding lush thru my open back 112 wideboy cab loaded with an Eminence Legend 1258. Just waiting on the pine combo cab to be finished (BG 'da man) and I've already purchased a re-coned 15" JBL K130 from an NZG member just for this project. I won't sound like SRV but I know one guy that will! And for those amp guts voyeurs, here's a couple of pics of the finished product.
Finished Chassis Topside.jpg (154.69 KiB) Viewed 5438 times
Finished Chassis Gutshot.jpg (221.96 KiB) Viewed 5438 times
My Blackstar ID core’s power supply has died, so I’m thinking about turning it into a powered cab - has anyone had any luck with the little cheap Class D modules, based on TPA3116 or similar IC’s?