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Post by jazznoise on Feb 27, 2018 4:06:32 GMT -6
So I recently got a deal on a Bugera 1960 infinium head, with the post phase inverter master volume and all. I know it's Behringer, but with what people now pay for a Peavey Bandit I'm just gonna enjoy owning a big tube amp. Sounds really good especially with drive pedals, but there's a good deal of noise and the breakup onset is way too quick (about 3!).
So it's got me thinking of switching to something like a 12AY7 for the input (what's used in a bassman, I beleive?). I know it's not technically correct to swap a tube without changing the biasing, but I'm just curious as to the experience of others.
Then on the noise end, will upgrading my preamp tubes like the Russian EHX ones make an improvement? It seems to be independent of the power stage.
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Post by Deleted on Feb 27, 2018 5:17:46 GMT -6
Preamp tubes can be changed without rebiasing, but will change the gain and tone. If you buy preamp tubes that have been screened for low noise it could improve things, but there are a LOT of other factors affecting noise as well. bowie on here has supplied all the tubes for my DR clone, and I've been very happy with the results. |
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Post by jazznoise on Feb 27, 2018 18:23:10 GMT -6
Thanks for the reply!
In terms of changes in tone, how so? I get that the plate resistance will be different, so the dampening factor for any filters following could be lower, but is there a distinct consistent change you could expect or predict?
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Post by ragan on Feb 27, 2018 18:26:34 GMT -6
So I recently got a deal on a Bugera 1960 infinium head, with the post phase inverter master volume and all. I know it's Behringer, but with what people now pay for a Peavey Bandit I'm just gonna enjoy owning a big tube amp. Sounds really good especially with drive pedals, but there's a good deal of noise and the breakup onset is way too quick (about 3!). So it's got me thinking of switching to something like a 12AY7 for the input (what's used in a bassman, I beleive?). I know it's not technically correct to swap a tube without changing the biasing, but I'm just curious as to the experience of others. Then on the noise end, will upgrading my preamp tubes like the Russian EHX ones make an improvement? It seems to be independent of the power stage. Wait, are Peavey Bandit's facing upward pressure?  I have a couple buddies who have had Bandit's since we were in high school. Man, they get some filthy tones out of those things! |
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Post by Tbone81 on Feb 28, 2018 9:29:30 GMT -6
Your preamp tubes are a big part of the tone of the amp. Some tubes will brighter, darker, quieter, have better low end, etc. I couldn't tell you the technical reasons why but from experience it can definitely make a noticeable difference. I like NOS Jan Philip's or Jan GE 12ax7's a lot for these duties.
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Post by jazznoise on Feb 28, 2018 10:01:31 GMT -6
Your preamp tubes are a big part of the tone of the amp. Some tubes will brighter, darker, quieter, have better low end, etc. I couldn't tell you the technical reasons why but from experience it can definitely make a noticeable difference. I like NOS Jan Philip's or Jan GE 12ax7's a lot for these duties. I get you, but also don't  I'm deliberately changing to 12AY7's to get more headroom out of the preamp stage. I was hoping for some specific idea of the tonal change from a 12AX to 12AY, but I'm starting to see it's probably just not that simple. |
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Post by mrholmes on Feb 28, 2018 10:05:33 GMT -6
I change all my 12AX7s to 5751 = 30% less gain.
The Amp stays longer "clean" and the "tone" kicks in later done by the second gain stage.
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Post by johneppstein on Feb 28, 2018 11:49:43 GMT -6
Your preamp tubes are a big part of the tone of the amp. Some tubes will brighter, darker, quieter, have better low end, etc. I couldn't tell you the technical reasons why but from experience it can definitely make a noticeable difference. I like NOS Jan Philip's or Jan GE 12ax7's a lot for these duties. I get you, but also don't I'm deliberately changing to 12AY7's to get more headroom out of the preamp stage. I was hoping for some specific idea of the tonal change from a 12AX to 12AY, but I'm starting to see it's probably just not that simple. Well, that's kind of a drastic change - the 12AX7 has a gain of 100 whereas the AY has a gain of only 45. www.300guitars.com/articles/preamp-tube-gain-factors-and-substitution-chart/I'd recommend trying something a bit less extreme for starters - maybe a 12AT7 or a 5751. Also the change may not be quite what you expect. We tried some of this sort of tube swapping with my lead guitarist's Princeton Reverb II (which is a 40 watt amp despite the "Princeton" moniker) and were not happy with the results, but YMMV. (Our consernsus was that it made the amp "wimpy".) Incidentally, it's the older tweed Bassmans that used the AY since Leo figured that the signal from a bass would tend to be hotter than that from a guitar, but many guitar players swap it out for an AX. Piggyback Bassmans from the brownface 6G6 on use a 12AX7/7025. (The 7025 is a lower noise 12AX7.) It kinda seems to me that swapping to a 12AY7 and using a drive pedal is probably like pissing into the wind.... |
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Post by Tbone81 on Feb 28, 2018 14:32:40 GMT -6
Your preamp tubes are a big part of the tone of the amp. Some tubes will brighter, darker, quieter, have better low end, etc. I couldn't tell you the technical reasons why but from experience it can definitely make a noticeable difference. I like NOS Jan Philip's or Jan GE 12ax7's a lot for these duties. I get you, but also don't I'm deliberately changing to 12AY7's to get more headroom out of the preamp stage. I was hoping for some specific idea of the tonal change from a 12AX to 12AY, but I'm starting to see it's probably just not that simple. Yeah there's no blanket answer here, you just got to try it and see. For example, Just changing from one brand 12ax7 to another (like JJ's to Mullards) will have a change in tone. Changing from one type to another (12ax7 to 12au7 etc) is yet another variable. My suggestion: but a couple different tubes and try them out. See what you like. |
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Post by bowie on Feb 28, 2018 17:01:38 GMT -6
Your preamp tubes are a big part of the tone of the amp. Some tubes will brighter, darker, quieter, have better low end, etc. I couldn't tell you the technical reasons why but from experience it can definitely make a noticeable difference. I like NOS Jan Philip's or Jan GE 12ax7's a lot for these duties. I get you, but also don't I'm deliberately changing to 12AY7's to get more headroom out of the preamp stage. I was hoping for some specific idea of the tonal change from a 12AX to 12AY, but I'm starting to see it's probably just not that simple. Here's some generalizations (because I believe in keeping it simple). Tone-wise, creating more headroom tends to thin the tone. 12AX7s usually have a low-mid/upper-bass push and subtle compression. Changes in gain and bias as you go lower on the mu chart often lean out the tone. But, then you have brands to consider. A 12AT7 will usually sound thinner than a 12AX7 when used in the same circuit, but something like a vintage Mullard 12AT7 might actually sound thicker because of the nature of those tubes. The construction and materials used give them their own character. All tubes are this way, though modern production pieces tend to have a more similar character to them. |
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Post by svart on Mar 1, 2018 7:29:09 GMT -6
My bassman had a AX7 in the preamp spot. I liked it.
I also had a 1960, which is a 1959 Plexi clone. Sounds GREAT if you want that plexi sound. I found that the OUTPUT tubes had a lot more to do with the overall tone thickness than the preamp tubes.
Bugera amps sound fine. I have 2 of them currently, and they sound exactly like the amps they're cloned from. I've had 4 of them over time.
HOWEVER..
They have a tendency to fail with strange problems. My TRIREC (triple rectifier clone) has failed with 2 different resistors going open (but not burned) and a diode going short (but not burned). And recently developed a problem with the channel switches not responding.. Guess I have to crack it open again..
My 6262 (6505 clone) has had a problem with a resistor going open (but not burned) as well.
They are FULL of cables too. Some of the older ones had connectors without any kind of clips holding them together, so they ended up coming loose all the time.
I ended up trading the 1960 because it sounded a lot like my other marshall clone, my Peavey Butcher, that's been modded to be exactly a JCM800 2204 super lead.
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Post by EmRR on Mar 1, 2018 9:20:12 GMT -6
The taper of the volume pot has a lot to do with headroom perception. A lot of older Fenders had a taper with a wider more centered sweet spot, and that pot taper was not available for years. Mojo and probably some others brought that taper back, I'm sure there's a handful of places you can get it from now.
A point on gain that's not widely understood. The gain charts are for theoretical conditions with minimal loading on the tube, the more the circuit loads it down (real world), the less gain there is and the closer a 12AY7 is to a 12AX7 in practice. You never get a gain of 100 out of a 12AX7 in reality. A 12AX7 in a 12AY7 slot may have less gain than a 12AY7 in that same slot due to the loading mismatch.
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Post by jazznoise on Mar 2, 2018 6:30:29 GMT -6
Right, that's the whole issue of the output impedance of the tubes. However I'd assume if the filter network created a bigger load than the amplifier could take, then I'd assume that would also increase the distortion. johneppstein the idea is to introduce dynamic range and be able to use a mix of pedal and amp drive when needed. The other option is to use a pad before hitting the input stage, but that seems like it's just going to cause more noise issues. |
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Post by johneppstein on Mar 2, 2018 13:34:22 GMT -6
Right, that's the whole issue of the output impedance of the tubes. However I'd assume if the filter network created a bigger load than the amplifier could take, then I'd assume that would also increase the distortion. johneppstein the idea is to introduce dynamic range and be able to use a mix of pedal and amp drive when needed. The other option is to use a pad before hitting the input stage, but that seems like it's just going to cause more noise issues. I've just found that swapping in lower gain tubes doesn't work very well - it has adverse effects on tone and makes the amp's response somewhat wimpy. I'd be more likely to try an actual minor mod to the amp - increasing the value of the cathode resistor in the V1 position a little bit to reduce the gain of the stage. |
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Post by jazznoise on Mar 4, 2018 7:50:56 GMT -6
If changing the tube doesn't work, I might try reducing the cathode resistor. I think I'd have to more or less halve the gain, to get the same result - we'll see!
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Post by notneeson on Mar 5, 2018 9:10:14 GMT -6
I don't know the Bugera, but just for fun— here's another theoretical cause of spongey, early break up: undersized output transformer.
I own a 68 Bandmaster Reverb. Stock it is a serious one trick pony, kind of cool, but limited. My tech put an enormous Ampeg output transformer in it and now it has headroom for days.
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Post by johneppstein on Mar 5, 2018 15:43:51 GMT -6
I don't know the Bugera, but just for fun— here's another theoretical cause of spongey, early break up: undersized output transformer. I own a 68 Bandmaster Reverb. Stock it is a serious one trick pony, kind of cool, but limited. My tech put an enormous Ampeg output transformer in it and now it has headroom for days. The usual mod is to use a Bassman transformer. The Bandmaster unit is definitely wimpy. |
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Post by notneeson on Mar 5, 2018 17:52:01 GMT -6
I don't know the Bugera, but just for fun— here's another theoretical cause of spongey, early break up: undersized output transformer. I own a 68 Bandmaster Reverb. Stock it is a serious one trick pony, kind of cool, but limited. My tech put an enormous Ampeg output transformer in it and now it has headroom for days. The usual mod is to use a Bassman transformer. The Bandmaster unit is definitely wimpy. Yep. My guy, when he was still working on amps, was an interesting combo of musician/junk man/aspiring EE. Although this is was before he went back to school and got a more lucrative engineering job. |
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Post by johneppstein on Mar 5, 2018 21:02:39 GMT -6
If changing the tube doesn't work, I might try reducing the cathode resistor. I think I'd have to more or less halve the gain, to get the same result - we'll see! INCREASING the cathode resistor. Reducing it would increase the gain. |
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Post by jazznoise on Mar 6, 2018 8:53:52 GMT -6
Sorry, yeah, I was half asleep replying. That said the more I think, increasing the amount of shunt feedback will linearize the response of the tube too. That's also going to change the sound, and the overdrive characteristic. I think my options are really preamp tube swap, phase inverter tube swap or attenuation of the input signal.
Bit of a minefield, really!
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Post by EmRR on Mar 6, 2018 9:31:25 GMT -6
Yeah that's gonna require experimentation.
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Post by jazznoise on Apr 22, 2018 7:13:27 GMT -6
So I went and did it and swapped the 12ax7 out for a 12AT. Definitely prefer it, much more clean headroom. Much more usable amp now Imo. Also swapped the bugera 12ax7s for some EHX ones, no harm done.
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I'm deliberately changing to 12AY7's to get more headroom out of the preamp stage. I was hoping for some specific idea of the tonal change from a 12AX to 12AY, but I'm starting to see it's probably just not that simple.
