Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Giovanni on June 29, 2020, 10:49:48 am
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Hello, I am new to the forum. I have been reading other members posts for a while, due to my interest in tube amps.
Some months ago I made my first build, a 5f1 champ. The amp was built from scratch and was a success.
Recently I decided to expand on it, by adding a tone knob and a reverb circuit. The tone knob works just fine. The reverb circuit is inspired by a layout I saw some guy post on the Telecaster reissue page. He himself got his circuit by modifing Tubenitīs.
However, I am having lots of troubles with the reverb. Thing is, there isnīt any. The amp sounds pretty much as it used to, but when I turn the reverb knob up, itīs like a distortion/fuzz that gets higher and higher. Also, if I crank the amp volume all the way up I get a high pitch squeal, regardless if I have the reverb on or off.
I have trying troubleshooting and checking components, but everything seems to work fine. I checked the tank into another amp, no problems. Doesnīt help either to get another thank into the 5f1, still sounds the same. I tried unplugging the tank all together and thereīs no change in the sound. In fact, it seems as if the signal is bypassing the tank somehow.
I really have no idea what the problem is. I draw a schematic of the reverb circuit, attached to the post.
I hope anybody will help me in finding out what the problem is. Thank you in advance.
Best regards,
Giovanni
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Also, if I crank the amp volume all the way up I get a high pitch squeal, regardless if I have the reverb on or off.
pull the reverb tube, still scream?
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Nothing wrong with the schematic you posted, except maybe the 3.3M resistor. We need to see the entire schematic so we know exactly how your reverb circuit interfaces with the 5F1 circuit.
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Here is the schematic. Itīs borrowed from Tube Amp Doctor. I highlighted the B+ nodes I used, and the send and return for the reverb.
I turned the amp on the check on that squeal noise, and it appears to be gone now, both with or withour the reverb tube.
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both with or without the reverb tube.
I've had bad 'tube seating" scream at me, don't take it personal :icon_biggrin:
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Haha, didnīt even know that could happen :laugh: thanks. Thatīs one problem out of the way.
Still getting that fuzzy distorted effect from the reverb circuit, with no response from the tank
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You show the 1nF capacitor connected directly to pin 2 on the driver tube, but it's not really like that when you wired it, right?
The full schematic didn't appear on my computer.
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You show the 1nF capacitor connected directly to pin 2 on the driver tube, but it's not really like that when you wired it, right?
The full schematic didn't appear on my computer.
I see I forgot to add the file to my comment. It should be uploaded now.
The 1 nF cap is going to a terminal strip lug which is connected to the pin 2.
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The 1 nF cap is going to a terminal strip lug which is connected to the pin 2.
That's OK. But, your drawing shows the 1M resistor on the wrong side of the 1nF cap. That 1M must be ***ELECTRICALLY*** connected to the tube grid pin 2. That doesn't necessarily mean the resistor must be physically connected to the socket.
That 3.3M resistor is way too big for the send/return points. Try a 100K instead and get rid of that 10pF cap.
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The 1 nF cap is going to a terminal strip lug which is connected to the pin 2.
That's OK. But, your drawing shows the 1M resistor on the wrong side of the 1nF cap. That 1M must be ***ELECTRICALLY*** connected to the tube grid pin 2. That doesn't necessarily mean the resistor must be physically connected to the socket.
That 3.3M resistor is way too big for the send/return points. Try a 100K instead and get rid of that 10pF cap.
So the 1 M must be between the 1 nF and the socket?
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One end of the 1M ELECTRICALLY connects to the socket pin 2.
The other end of the 1M ELECTRICALLY connects to chassis.
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One end of the 1M ELECTRICALLY connects to the socket pin 2.
The other end of the 1M ELECTRICALLY connects to chassis.
I see.
This is quite a puzzler really. The tank works so far. The tube is working and warming up fine. I have no impedance measuring device, but I got ohm readings of 1030 from the primary and 2,2 from the secondary, which as far as I understand is acceptable. Also no leakage to ground. The circut is pretty much as I drawn it, only I have now removed the 3,3M resistor in favor of a 100k, removed the 10 pF cap and ensured that the 1M resistor is connected to pin 2. The distortion is now gone, but still no reverb, and no big frightening sound if I hit the tank.
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Ok, somehow I got the reverb to work. The problem now is that the amp has become very fuzzy sounding, it starts as soon as the volume is about halfway and doesnīt go away even if the reverb is all the way down. Any thoughts?