I have a pv classic 30, a newer series II one thats redesigned with a single circuit board. I found that with the band i had the volume up to the point theres almost no headroom left so that volume boosts in the loop do little and even front end gain boosts don't do much because they just make it muddy. I realize a 30 watt amp isn't going to have a ton of HR, but wasn't sure where the issue is happening till i put a active device in the loop and turned the master way up to band level. Dropped the volume in the device so it was bedroom volume which yielded a tone that was like the device removed and mater down to home levels. That told me the headroom issue is not the gain stages. The loop is after the stack and before the PI. So the PI, EL84s, and speaker are all suspect. Granted the speaker is a slightly low dB speaker (96) but tat shouldn't be the issue because i tried a 102 dB and while louder and cleaner it wasn't a LOT more. So the typical 97-98 dB speaker shouldn't make any difference. That leaves the PI and EL84s.
So my question is, what possibilities can i consider to get even just a bit more headroom? It's not biaes real hot because the voltages i see at home, rehearsal, and i assume the venues are so wide (117-125vac) that i'm afraid to set it above 60%, maybe 70 at most. That leads to the first question.....will hotter bias make any difference in headroom? Second question, can you recommend anything i can do to help with this issue circuit wise? Schematic added. Oh, and it has new JJ 84s and the preamp tubes are all good and i've tried many, but obviously the PI is the only place that could matter. I tried a LPS long plate there to no avail. Ideas?
headroom and bias
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iknowjohnny
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headroom and bias
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Re: headroom and bias
You need to get busy with a sig gen, scope and dummy load.
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Stevem
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Re: headroom and bias
I general the hotter output tubes are biased passed the point where they give a respectable punchy clean sound then setting them for a hotter bias only serves to us up power supply current and the tubes themselves faster.
Thats current other wise that could be used to produce more RMS wattage before clipping starts in the output section due to plowed supply sag.
You should experiment with the bias setting to find out exactly where that tipping point is in your amp.
And as posted a O scope and a signal generator and a 8 ohm load test resistor would be of great help to you as it would reinforce in a visual way what your hearing and feeling with the amp.
I forget what size/ mass output transformer that amp has, but it’s likely part of the lack of clean head room issue also because its size was chosen to saturate and add distortion of its own also.
You might find a OT of bigger mass that would still bolt in .
Thats current other wise that could be used to produce more RMS wattage before clipping starts in the output section due to plowed supply sag.
You should experiment with the bias setting to find out exactly where that tipping point is in your amp.
And as posted a O scope and a signal generator and a 8 ohm load test resistor would be of great help to you as it would reinforce in a visual way what your hearing and feeling with the amp.
I forget what size/ mass output transformer that amp has, but it’s likely part of the lack of clean head room issue also because its size was chosen to saturate and add distortion of its own also.
You might find a OT of bigger mass that would still bolt in .
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
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iknowjohnny
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Re: headroom and bias
I don't have a scope or even know how to use one. I just thought maybe theres something that might help aside for more and louder speakers. I guess micing is in order, tho i hate what PA's usually do to my tone. A bigger OT is gonna need a bigger PT i believe.
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Stevem
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Re: headroom and bias
No, what your assuming is not the case.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: headroom and bias
I have a problem with the term "headroom" in guitar equipment.
Headroom means something like there's a little more (something) left if you're already working at maximum. That is not how we treat guitar amps as a general rule. We (as a group) turn them up all the way and then want more.
If your amp is working correctly, putting out its specified power, and you need more sound pressure level, you're kind of stuck with getting more efficient speakers or getting a higher power amp. There is only so much adding more signal level to the input of the power amp before it's already putting out all it can. When you get there, more input signal (like boost from a loop) will not push more power out, it will only make the amp distort.
96db at 1W/1m is, as you say, not very efficient. Some Celestions I've seen claim 106db.
If the amp will drive external speakers and more of them, try hooking on an additional cab or two. You might get better acoustic efficiency that way. Or the external speakers may be more efficient.
Headroom means something like there's a little more (something) left if you're already working at maximum. That is not how we treat guitar amps as a general rule. We (as a group) turn them up all the way and then want more.
If your amp is working correctly, putting out its specified power, and you need more sound pressure level, you're kind of stuck with getting more efficient speakers or getting a higher power amp. There is only so much adding more signal level to the input of the power amp before it's already putting out all it can. When you get there, more input signal (like boost from a loop) will not push more power out, it will only make the amp distort.
96db at 1W/1m is, as you say, not very efficient. Some Celestions I've seen claim 106db.
If the amp will drive external speakers and more of them, try hooking on an additional cab or two. You might get better acoustic efficiency that way. Or the external speakers may be more efficient.
"For every complex problem there is an answer that is clear, simple, and wrong"
H. L. Mencken
H. L. Mencken
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iknowjohnny
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Re: headroom and bias
Well, thats what i've been looking at doing but it's anything but ideal for me on several levels. But i'm already on the hunt to load a empty 1x12 i have. I don't expect that to make much difference unless it's like the eminence i recently tried (102.3dB/150w) and hated. So i'm looking at something thats more efficiant than the internal speaker which tone wise i LOVE, but not a lot more. Maybe 80-100w and 98-100dB. I just like the stock one so much i fear speakers that will sound a lot different and trying that eminence taught me that while in the past i used many efficiant speakers, (EV12L for example) with this amp thats not what i like. So something a bit more efficiant will hopefully let me get at least some perceived loudness so i don't have to max the master. Put it this way....as it is now the amp isn't ideal as headroom goes, but i can get by with it as is. So it wouldn't take a lot.
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iknowjohnny
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Re: headroom and bias
This is a difficult amp to repair or modify. If it ain't doing what you want, it might be better off in the hands of someone who does like it as is.
Also, it ought to be pretty loud already. If you need more clean power out of it, look for something with a pair of 6L6's instead, like a good used Blues DeVille or similar that's pushing about 55 wats of power. Or if you really need clean power, 4x 6L6's, like a Twin.
The PI is a "concertina" type, and the other half of the tube is an unbypassed common cathode preamp stage. The schematic suggests a somewhat cold bias point on the output quad.
It's possible to build a sparklier, cleaner 4x EL84 amp, but it might be a lot easier to just shine her up pretty and head to the nearest guitar shop and horestrade for something else.
FWIW, I regularly play with a full band in a club, with an 18w Blues Jr, as does the other guitarists, and that's plenty loud
Also, it ought to be pretty loud already. If you need more clean power out of it, look for something with a pair of 6L6's instead, like a good used Blues DeVille or similar that's pushing about 55 wats of power. Or if you really need clean power, 4x 6L6's, like a Twin.
The PI is a "concertina" type, and the other half of the tube is an unbypassed common cathode preamp stage. The schematic suggests a somewhat cold bias point on the output quad.
It's possible to build a sparklier, cleaner 4x EL84 amp, but it might be a lot easier to just shine her up pretty and head to the nearest guitar shop and horestrade for something else.
FWIW, I regularly play with a full band in a club, with an 18w Blues Jr, as does the other guitarists, and that's plenty loud
Re: headroom and bias
Ok, I suggest you take it to someone who has, and ask them to check the amp is working correctly.
https://www.justgiving.com/page/5-in-5-for-charlie This is my step son and his family. He is running 5 marathons in 5 days to support the research into STXBP1, the genetic condition my grandson Charlie has. Please consider supporting him!
Re: headroom and bias
Get another 30 and play both of them as physically close together as you can. Should get another 6 dB.
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flemingmras
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Re: headroom and bias
Get a 100 watter. You'll get just over +5dB more headroom.iknowjohnny wrote: ↑Sat Jun 20, 2026 6:17 pm So my question is, what possibilities can i consider to get even just a bit more headroom?