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Understanding What My Tubes Do

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Audio Refugee

Understanding What My Tubes Do
« on: 3 Dec 2016, 05:01 am »
Hi AC, I'm new here and new to tube amps. I've acquired a Jolida 202A. I'd like understand which tubes do what on my amp, and was hoping someone here might be school me. I called Jolida, ordered, received and read the manual. It tells me that I have four 6CA7/EL34s, two 12AX7s and two 12AT7s.

I might like to play with tube rolling, but before I do I'd like understand what I'm doing. I understand that rolling the smaller 12As provides more noticeable changes than the larger power tubes. At least that's what I've read in a few places. It's not clear if the AXs or the ATs are the best roll, or both. Any info, links, primers, tubes for dummies articles, opinions, etc. are much appreciated. :lol:
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Tone Depth

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Re: Understanding What My Tubes Do
« Reply #1 on: 3 Dec 2016, 05:06 am »
Tubes amplify the voltages in the analog signal from your source so they can drive your speakers.
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JackD

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Re: Understanding What My Tubes Do
« Reply #2 on: 3 Dec 2016, 05:35 am »
The AX7's which are the preamp tubes are the most significant roll and then the AT7's which are the amps driver tubes.  Most of the current production power tubes are made in just a few Chinese or Russian plants and are not all that dissimilar.  The replica Mullard EL-34's are probably the best of the bunch and readily available at reasonable prices.
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Audio Refugee

Re: Understanding What My Tubes Do
« Reply #3 on: 3 Dec 2016, 06:03 am »
Quote from: JackD on  3 Dec 2016, 05:35 am
The AX7's which are the preamp tubes are the most significant roll and then the AT7's which are the amps driver tubes.  Most of the current production power tubes are made in just a few Chinese or Russian plants and are not all that dissimilar.  The replica Mullard EL-34's are probably the best of the bunch and readily available at reasonable prices.

Jack, thank you. You mention the ATs are a more significant roll. In what way? The AXs are drivers. As in providing bass?
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JackD

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Re: Understanding What My Tubes Do
« Reply #4 on: 3 Dec 2016, 06:53 am »
You've got it backwards.  The AX's are the preamp tubes and are first in the chain in an integrated amp.  They set the tone for what follows and are the most significant change.  In the Jolida the AT's are the "driver tubes" for the amp section and can impart a slight change in the flavor for the amp section.  The power tubes have the least value in sound change as long as they are functioning properly  They are the last thing to change once you get the other tubes in line.
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FullRangeMan

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Re: Understanding What My Tubes Do
« Reply #5 on: 3 Dec 2016, 09:58 am »
I will second JackD:
12ax7 are input tubes(gain)
12at7 are driver tubes (drive the EL34)
EL34 are the output tubes (power tubes)
Output circuit are PP, rectification are SS.
A nice art-deco looking amp.
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Audio Refugee

Re: Understanding What My Tubes Do
« Reply #6 on: 3 Dec 2016, 04:50 pm »
Now it's beginning to make some sense. Thanks again JackD and Full Range. Wondering in and out of circles here... I have an enormous amount to learn. Who knew something so simple looking with only one switch and two knobs could be so complicated. Tubes, isolation, positioning, treatments, speaker types, power, and on and on and on. It's a bit overwhelming. Yet, I'm beginning to understand why this hobby is so intoxicating to so many. :duh:

The stickies in this circle led me to some neat sites that speak to the different brands and differences between 12AX7s. Big price swings. Read other articles about counterfeits. Like I said... I have a lot to learn.
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Graywulf

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Re: Understanding What My Tubes Do
« Reply #7 on: 14 Jan 2017, 10:48 am »
not wanting to start an argument as I am not a 'tech' just an 'end user' for a couple of decades...

I would partly disagree about the sound being effected by the output tubes to a minimal extent... {caveat emptor} good quality over cheap n nasty of the same tube type is obvious.
 But changing the tube type can also have a quite 'dramatic' effect. In 2007 after much 'soul searching' I sold my beloved Radford STA100 {this was due to back then KT88's were just not up to the amplifier, 600v anode/screen which a genuine GEC KT88 was made to handle, it ate voraciously modern KT88's with a constant supply of sacrificial resistors being replaced}.
  I bought a MingDa MC34AB which has indeed over time proven to be a 'good un' in the Hifi world. I replaced the preamp and splitter tubes with 'old tubes' for a significant difference. Maybe I missed the KT88 'sound'? as the Ming uses 8XEL34. I upgraded in 2008 to JJ KT77;s.. they had a profound alteration on the sound, more 'athletic' cleaner, a bit more punch.. Now I will accept that possibly the blue Jinvina EL354's were not 'top shelf' tubes, but there was a substantial improvement.
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FullRangeMan

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Re: Understanding What My Tubes Do
« Reply #8 on: 14 Jan 2017, 10:58 am »
After the power tube there is the OPT to give the final word in the sound character.
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