Quick explanation of cathode bias using a constant current sink:
https://books.google.com/books?id=QdGJlyCb7UsC&pg=PA196&source=gbs_toc_r&cad=4#v=onepage&q&f=false
This is from "Valve Amplifiers" 4th Ed. by Morgan Jones.
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https://books.google.com/books?id=QdGJlyCb7UsC&pg=PA196&source=gbs_toc_r&cad=4#v=onepage&q&f=false
This is from "Valve Amplifiers" 4th Ed. by Morgan Jones.
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My Baby Huey is broken
After functioning (and sounding) just fine for the last 10 months, all of a sudden this evening one channel started squealing. It sounded like a cross between fingernails on a blackboard and breaking glass. It had just been loping along with the radio playing at low volume. I immediately killed the volume - the noise continued - and then I killed the power switch. As the voltage dropped away the general screech resolved into what sounded like a tonal of something like 5kHz. I've got no idea what harmonics were there too, but it's probably not diagnostic anyway.
Nothing smells horrible, there was no smoke and I can't see any signs of damage. The fuses didn't blow in the few seconds before I shut it down.
Is this how valves normally fail? Is it some other "obvious" thing? I changed the Mullards out for Genalex about 8 weeks ago when I replaced the output Hammond 1615 transformers with James 6228HS, but there has been no problem 'til now.
Since this is my first tube amp, it has now become my first attempt at fixing one. Any advice on the most effective diagnosis strategy would be very welcome. Thanks
After functioning (and sounding) just fine for the last 10 months, all of a sudden this evening one channel started squealing. It sounded like a cross between fingernails on a blackboard and breaking glass. It had just been loping along with the radio playing at low volume. I immediately killed the volume - the noise continued - and then I killed the power switch. As the voltage dropped away the general screech resolved into what sounded like a tonal of something like 5kHz. I've got no idea what harmonics were there too, but it's probably not diagnostic anyway.
Nothing smells horrible, there was no smoke and I can't see any signs of damage. The fuses didn't blow in the few seconds before I shut it down.
Is this how valves normally fail? Is it some other "obvious" thing? I changed the Mullards out for Genalex about 8 weeks ago when I replaced the output Hammond 1615 transformers with James 6228HS, but there has been no problem 'til now.
Since this is my first tube amp, it has now become my first attempt at fixing one. Any advice on the most effective diagnosis strategy would be very welcome. Thanks
Hi psupine,
One of the advantages of building your own amp is that you stand a good chance of fixing it yourself
I would remove the valves taking note of which socket they came from. Power up the amp and measure the voltages at the pins of each socket with respect to ground. This can be done from above. Look for a significant difference in voltage ( 10% ) between the good and the bad channel. If nothing significant is found then I would check the valves.
With the power off put the valves from the good channel into bad channels sockets. Power up being ready to turn off imediately if the bad sound returns. If all is well then it's likely you have a faulty valve.
One of the advantages of building your own amp is that you stand a good chance of fixing it yourself
I would remove the valves taking note of which socket they came from. Power up the amp and measure the voltages at the pins of each socket with respect to ground. This can be done from above. Look for a significant difference in voltage ( 10% ) between the good and the bad channel. If nothing significant is found then I would check the valves.
With the power off put the valves from the good channel into bad channels sockets. Power up being ready to turn off imediately if the bad sound returns. If all is well then it's likely you have a faulty valve.
Hi,
I want to bild the baby huey now (Baby Huey PP EL84 amplifier - diyAudio).
Two questions about the current source.
1. I have a 13V AC winding on my trafo. Do I have to modify the circuit for the constant current source of the ECC803S, because my voltage supply for the CCS will be higher?
2. Where do I have to connect the "0V at ECC803S" Pin of the CCS at the main circuit?
I would use the star ground ("0V from other channel")?
I want to bild the baby huey now (Baby Huey PP EL84 amplifier - diyAudio).
Two questions about the current source.
1. I have a 13V AC winding on my trafo. Do I have to modify the circuit for the constant current source of the ECC803S, because my voltage supply for the CCS will be higher?
2. Where do I have to connect the "0V at ECC803S" Pin of the CCS at the main circuit?
I would use the star ground ("0V from other channel")?
Stero to Mono Switch
Hi all,
Have found a wonderful old radiogram cabinet to put my Baby Huey amp into, and would like the the options of switching between stereo outputs to separate external speakers, or to a mono speaker in the cabinet.
Suggestions on how best to achieve this?
Thanks in advance, Malcolm
Hi all,
Have found a wonderful old radiogram cabinet to put my Baby Huey amp into, and would like the the options of switching between stereo outputs to separate external speakers, or to a mono speaker in the cabinet.
Suggestions on how best to achieve this?
Thanks in advance, Malcolm
Attachments
Malcolm,
Do as 6L6 suggests
OR
The Issues are:
For separate external speakers just run speaker outputs as "normal".
To run a single internal speaker you would want to:
1) combine the 2 channels from the preamp to drive one channel of the BH power amp. This might be able to be done in your preamp or may require an "intermediate" mixing amp.
2) Switch the internal speaker to that BH channel output.
The remaining problem is then what to do with the un-used channel of the BH power amp. Switching it off maybe difficult so I would suggest that you do two things:
a) Switch it's input to signal ground - This could be done in the "mixing" box.
b) Switch a dummy load resistor of the nominal speaker impedance across its speaker output. This ONLY needs to be a low power resistor since it is not going to be driven.
You could combine the mixing function and speaker switching into a single box driven by a 4 pole switch.
I would normally suggest an OPA2134 (quad) or OPA2132 (dual) Audio Op Amp for the mixing box but in this case its max power supply of +/- 5V may be a problem with peak signal delivery into the BH power amp although the mixing box clipping at around X2 the BH amps clipping point says otherwise so maybe OK. Otherwise choose a decent FET input Opamp which will run from +/-15V rails.
My random ravings - hope there is something usefull to you.
Cheers and Merry Xmas to all.
Ian
P.S. For simple mixers etc. I normally go to ESP first to see what he has
http://sound.westhost.com/projects-0.htm#mix
Also I looked up the datasheet for OPA2132PA (the 8 pin DIP version) and it says +/- 18V rails max so ignore comment above. It will be fine
http://www.ti.com/lit/ds/symlink/opa2132.pdf
Do as 6L6 suggests
OR
The Issues are:
For separate external speakers just run speaker outputs as "normal".
To run a single internal speaker you would want to:
1) combine the 2 channels from the preamp to drive one channel of the BH power amp. This might be able to be done in your preamp or may require an "intermediate" mixing amp.
2) Switch the internal speaker to that BH channel output.
The remaining problem is then what to do with the un-used channel of the BH power amp. Switching it off maybe difficult so I would suggest that you do two things:
a) Switch it's input to signal ground - This could be done in the "mixing" box.
b) Switch a dummy load resistor of the nominal speaker impedance across its speaker output. This ONLY needs to be a low power resistor since it is not going to be driven.
You could combine the mixing function and speaker switching into a single box driven by a 4 pole switch.
I would normally suggest an OPA2134 (quad) or OPA2132 (dual) Audio Op Amp for the mixing box but in this case its max power supply of +/- 5V may be a problem with peak signal delivery into the BH power amp although the mixing box clipping at around X2 the BH amps clipping point says otherwise so maybe OK. Otherwise choose a decent FET input Opamp which will run from +/-15V rails.
My random ravings - hope there is something usefull to you.
Cheers and Merry Xmas to all.
Ian
P.S. For simple mixers etc. I normally go to ESP first to see what he has
http://sound.westhost.com/projects-0.htm#mix
Also I looked up the datasheet for OPA2132PA (the 8 pin DIP version) and it says +/- 18V rails max so ignore comment above. It will be fine
http://www.ti.com/lit/ds/symlink/opa2132.pdf
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An off the shelf box like this:
2 Way Speaker Selector Switch | Switchers | AV Switchers & Converters | Sight & Sound - Home | PRODUCTS | AC1640 | Jaycar Electronics
Is available from many of the "usual suspects". To protect against no speaker connection while switching simply add say 220 Ohm resistors permanently wired to the amps speaker outputs. With a speaker connected very little power is "wasted" in that 220 Ohm but it is enough of a load to protect the amp with no actual speaker load.
Cheers,
Ian
2 Way Speaker Selector Switch | Switchers | AV Switchers & Converters | Sight & Sound - Home | PRODUCTS | AC1640 | Jaycar Electronics
Is available from many of the "usual suspects". To protect against no speaker connection while switching simply add say 220 Ohm resistors permanently wired to the amps speaker outputs. With a speaker connected very little power is "wasted" in that 220 Ohm but it is enough of a load to protect the amp with no actual speaker load.
Cheers,
Ian
I'm curious. Has anyone built a larger tube version, such as KT88 or EL34, and compared it to the EL84 or 6V6 designs? If so, I would like to know of your experience. The Baby Huey looks like a wonderful project, but I need a bit more power.
I have two Hammond 6.6k, 60 watt pp transformers and am looking for a circuit for them. They are overkill for my needs. I don't need more than 30 watts, and am looking for something that just sounds great and is easy to build.
Thank you
I have two Hammond 6.6k, 60 watt pp transformers and am looking for a circuit for them. They are overkill for my needs. I don't need more than 30 watts, and am looking for something that just sounds great and is easy to build.
Thank you
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