HT Studio 20 with 6L6's?

Discussion - HT Venue amplifiers. Inspiration from Studio to Stage.
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Voldaer
Posts: 1
Joined: Thu Mar 03, 2016 4:48 am

Thu Mar 03, 2016 5:40 am

Hello, I have a weird issue with an HT Studio 20 head that I was hoping someone on this forum might be aware of. I've searched all over the manuals, internet, and these forums and everything tells me that this amplifier has EL34 power tubes. I bought new tubes for it and when I opened it up to put them in I found it loaded with two 6L6's instead. I know that some amps can interchange between EL34 and 6L6 but I cannot find anything telling me that this amplifier is set up for that. I also cannot find anything about any sort of special releases or anything where it was configured with 6L6 instead of EL34. I emailed Blackstar yesterday but they have not responded yet. Is there anyone out there that is aware of this amp having 6L6's? Can I put EL34's in and set the bias and be good to go or do I need to exchange my EL34's for some 6L6's? If I have to use 6L6's does anyone know what I need to set the bias to? I cannot seem to find much of anything directly from Blackstar's published information other than basic specs, most of what I do know about this amp is some youtube videos that I watched of someone setting the bias on the combo version (which had EL34's!!).

Any insight or information someone could provide would be greatly appreciated. I've been searching for two days and have not found a single thing about this amp using 6L6's

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thephantum
Posts: 1160
Joined: Wed Jan 29, 2014 7:42 pm
Location: Virginia, United States

Thu Mar 03, 2016 8:17 pm

First of all, there is no such thing as a standard bias setting. The only proper way to set bias is to measure the plate voltage, do the calculation, set bias and then do it all over and over again until the amp is dialed in.

Theoretically you can use 6L6's in place of EL34's, but there are caveat's to that. Specifically, the 6L6 has a much lower maximum plate voltage then the EL34 (450V vs 800V). So as long as the plate voltage of an amp runs lower than 450V (which the HT-40 does), you can run them. The 6L6 also only has 2 grids to the EL34's 3 grids...but most El34 amps (including the HT-40) only use grids 1 & 2 anyway. So no big deals there either.

The big difference is that the 6L6 has a higher plate dissipation rate (30W vs 25W). That means it will bias differently than an EL34. In some cases, that difference means that the amp cannot provide enough bias current without modification. My experience with B* tells me that there is enough adjustment to dial in a high enough setting for a 6L6. That's not a definitive answer, juts my own opinion.

The only way to know for sure is to open up the amp, put in EL34's, measure plate voltage, do the math to see what bias should be and then try and set it. If you can't get it low enough for the EL34's. then the amp was modified.

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