6SQ7 EL34 Tube Audio Amplifier: Output Tube Voltage Test
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- čas přidán 18. 10. 2021
- Warning: Voltage testing a tube amp is dangerous. IF YOU ARE NOT 100% COMFORTABLE AND UNDERSTAND ALL SAFETY RISKS INVOLVED, DO NOT DO THIS!!!
In this video we power up the amp and check the internal voltages. I cover a few safety tips, you can see more here and there is MUCH more than is listed here on the subject.
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Here is a link to the tube bias calculator I like:
robrobinette.com/Tube_Bias_Ca...
and here is a basic Ohms Law calculator:
ohmslawcalculator.com/ohms-la...
This is a replicate of my personal favorite, a 6SQ7-EL34 amp with modifications to make it more "public friendly". This series will document the build in detail, explain all the design considerations, dig into tube data sheets and other criteria that makes this little amp sound so amazing!
I'll get the schematics and BOM up on the website this week as I start on the actual build series. - Jak na to + styl
Great stuff as usual.🙂
Every tibe amp owner needs to see this channel.
Can’t wait to see what you have for your next project
Nice demo of the safety aspects involved. Thanks!
Obviously this isn't all of them and like I state in the video, if you are new to this: using clip leads and powering the amp down between lead changes is even safer.
It’s ALIVE!!!! Great job 👏
Learning so much. Thank you
Great, Thanks for this lesson 👍
Superb Channel!! DIYer gonna love this channel. Applause. I will try to learn more about tube amp here but many things still difficult. Luckily YT can be replay
Very wise decision.
Great series! Any chance of seeing a schematic for this amp on your website soon? If it has key voltages annotated that would be even better!
Uploaded them to the website tonight. There are two versions of the power supply, the 2 choke version from my original and this 1 choke design I am building now, but haven't tested yet because I haven't finished the amp. I don't expect it to have any issues but...
www.skunkiedesigns.com/6sq7
@@SkunkieDesignsElectronics Thank you! Just confirming, if my maths is correct you are running about 1mA of bias through the 6SQ7. Is that correct?
@@SignorZukini Trying to get ahead of us? lol
It ends up being about 1.33mA measured. Looking just at the schematic: 0.2V across 160ohms is 1.25mA. But measured, the resistor is actually 158ohms and the voltage is 0.21V across it which equals 1.33mA. You really can't use the voltage across the plate load resistor because the Schade feedback also contributes to that voltage. This 1.33mA is just what I would expect looking at the load lines chart. I came to this bias point with some trial and error listening between -1.4 and -2.0V grid bias.
@@SkunkieDesignsElectronics thanks very much. Not getting ahead but was interested to know how much current is needed to drive an EL34!
My understanding of isolation transformers is that the electricity out of them is not ground referenced. Does that mean that if i touch one lead and my feet are grounded I won’t get electrocuted ?
Not that I want to try it .. just want to make sure I understand correctly
That is their purpose, to isolate the neutral from ground potential. They also protect any weird ground issues when using a scope. Know that using an isolation transformer doesn't make this "safe", just a little less dangerous.
I see others have asked if a Dummy Load is required… However, It does not look like you had a Dummy load connected to the amplifier… Did you have a Dummy Load connected while you were taking the voltages..?
It's always a good idea to have a dummy load connected when powering up a tube amp. I'm not going to swear I have never powered one up without them, and if there is no input signal it won't hurt the amp nor will that affect the voltages measured at idle. Given the input tubes aren't even installed yet, it's not possible for there to be any input signal nor could the amp oscillate. It does looks like you caught me making a mistake while recording a video, it's easy to get distracted.
Bottom line, always try to have a dummy load connected when powering up a tube amp. NEVER inject a signal into a tube amp with no load, that absolutely will damage it. If you do mistakenly power up an amp with no load on the output, as long as no signal was feed into it and the amp is stable, it's highly unlikely any damage will occur.
@@SkunkieDesignsElectronics Thank you for clarifying.. :) Believe me.. I don’t watch educational videos looking for mistakes.. I’m learning.. so I was just asking.. I have now learned that for one to be safe, use dummy loads.. however, if you are not injecting a signal, you can get away without using a dummy load, but not really recommended.. Thanks for your reply.. Great videos, btw..:)
Do you need a dummy load when taking these measurements/
Yes, a tube amp always need a load on the output to avoid damaging the output transformers.
Do you need dummy load to test
Absolutely. NEVER run a signal through a powered up tube amp without a load on the speaker jacks!
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Thank You For The Safety Tips Stephi Sweetie 💖 Love & Kisses To Dolly 🐶🐾🐕 Woof Woof 💖👄