Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: peacocksuit on May 06, 2026, 07:51:05 pm
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Hello, all. Just after some advice re a Tremo-Nator circuit which I've managed to get working in an amplifier in currently tinkering with. I've built the amp out of old bits, I've based the pre amp section on a Princeton 'reverb delete' schematic from the site robrobinette just to have something to reference as I'm not ofay with amp building enough yet to design my own circuits. The power stage however uses a transformer that originally powered EL34's in push pull. It puts out 400v AC unloaded. So I'm not using 6v6's but have instead been experimenting with different higher output tubes more akin to those which the transformer was designed to work with. I've stuck with grid bias as I initially tried to make the Princeton tremolo circuit work. However it's obviously designed to work with the lower output 6v6's in the Princeton and even then, from what I've read it seems the trem can be quite pinickity.
I did actually try some NOS 6П6С's which I've had in a draw for a long time and with a lot of trial and error with high resistor values on the bias board to get the operating point low enough for them, I did get the Princeton tremolo circuit to work. A bit. It was pretty weak though so I abandoned it went back to experimenting with 6L6GC's and EL34's.
I stumbled on a post and saw the Trem-onator mentioned so thought I'd try that instead and I've just managed to get it working.
I wasn't able to pick up the VCL571 (I have a place near me where I can collect same day) but they had another Optocoupler in stock a NSL-32SR3 which I've used instead.
I will l need to pick up a 50k pot for the intensity, I had some 250k pots already which I've tried but they don't seem to work (I only get the tremalo when the pot is turned to the extreme max position). For experimenting I just jumpered various resistors in place of the pot ranging from 50k down. I discovered though a bit of trial and error that the ground connection at the intensity pot wasn't needed, I've confirmed this doing some further reading on this forum. I have the prescribed 3m RA pot on for the speed control.
The Trem is definitely working! I experimented with inserting the Tremo-Nator are different positions in the circuit and settled on the grid of the Cathodine phase splitter, right after the decoupling capacitor. It seems to work well there.
I just need some help to perhaps tweak it a bit to get it working to it's full potential with my amp.
The first thing I noticed it that it doesn't seem to sound very 'smooth'. It's more like a choppy sound. Usually Tremolo modulates the volume in a way that sounds like it slopes up and down gently but this seems quite steep. It's not on 'or' off, it's got some slope/curve but it's sounds steep slope. It sounds almost like a pulse, if that makes sense? I'm hoping there might be something I can do to change that.
Also, the range of speed doesn't seem quite right at the moment. The speed pot does it's job, I can hear the speed decrease as I turn the dial as I'd expect and turns fully to the slowest end the effect stops. The issue is that it's not fast enough at the highest speed setting.
And lastly, I've noticed that the overall volume of the input signal increases quite a bit when I open the 'switch' (which is actually just a crocodile clip lead the optocoupler led and ground :icon_biggrin:). Even if the tremalo was fully turned to the slowest position, which kills the effect anyway, when opening the switch (foot switch on the schematic) there's a fair increase in the volume of the signal. It would be good to get some insight on that as well. Can anyone offer any help with any of these teething problems? I'd be really grateful.
Anyway, really pleased to have it up and running so big thanks to the original designer.
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Took 2 short videos of the fastest and slowest speeds to show how it sounds.
i=_E9cjKbqBkJuO0tS
i=02YdwIHmN4frZ3bn
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Thanks very much.. I'll have a play around with those values. Does the sound of the Trem in the videos generally sound as expected?
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Does the sound of the Trem in the videos generally sound as expected?
No it doesn't. Listen to the sound clips on my website...
https://sluckeyamps.com/trem/trem.htm
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Does the sound of the Trem in the videos generally sound as expected?
No it doesn't. Listen to the sound clips on my website...
https://sluckeyamps.com/trem/trem.htm
If I'm honest I had already visited and listened. It's obvious that it doesn't sound right :icon_biggrin:.
I understand that I need to change those to caps to change the speed. I'm not sure what will make it stop pulsing like it is now though. I was hoping someone could advise. Changing the speed is only half the issue.
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It can be a challenge to find the best way to connect the TON to a circuit. The attached pic shows how I would try to connect the TON to Robinette's modified PR. May still require a bit of experimentation to get it right.
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Thanks, Sluckey. Changing the values of those capacitors has definitely made an impact on the speed. I now have a much better range of speeds and more control over them. Unfortunately it still sounded choppy as before and also as before, the tremelo circuit significantly reduced the overall volume of the amplified signal when in circuit. I tried inserting the tremelo into the circuit at the point which you suggested but the result was exactly the same.
I happened upon a post by a member called Lectroid (hope I've spelled that right) who was struggling with his Princeton clone and managed to get good results after trying all manor of things by using the cathode of valve 1b as the insertion point. I tried this and viola! Not only does the Tremelo sound like your samples but it also doesn't make the overall signal reduce. I'm really pleased! I need to do a bit more experimenting with the capacitors but it sounds excellent 👍🏻
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I happened upon a post by a member called Lectroid (hope I've spelled that right) who was struggling with his Princeton clone and managed to get good results after trying all manor of things by using the cathode of valve 1b as the insertion point. I tried this and viola! Not only does the Tremelo sound like your samples but it also doesn't make the overall signal reduce. I'm really pleased! I need to do a bit more experimenting with the capacitors but it sounds excellent 👍🏻
Can you share a link to that post?
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I happened upon a post by a member called Lectroid (hope I've spelled that right) who was struggling with his Princeton clone and managed to get good results after trying all manor of things by using the cathode of valve 1b as the insertion point. I tried this and viola! Not only does the Tremelo sound like your samples but it also doesn't make the overall signal reduce. I'm really pleased! I need to do a bit more experimenting with the capacitors but it sounds excellent 👍🏻
Can you share a link to that post?
https://el34world.com/Forum/index.php?topic=28666.0