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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 10:47 am
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Remember, the plate voltages on the signal tubes (12AX7 & 12AT7) will also go up --- with a higher output rectifier. This may effect the tone more than increased plate voltages on the output tube. You can globally drop the anode voltages on the signal tubes, by changing the appropriate resistor(s) in the PSU rail.

A good example of this is how Fender ran a 22k-ohm rail resistor feeding the input tube plates of the 5F1 Champ. And a 10k-ohm resistor on the Champ (AA764). You'd be amazed at the change in tone and OD by simply changing the BF Champ's 10k-ohm to 22k-ohm. Voltage on the anode goes from ~220VDC to 150VDC. With a big difference in tone and overall response of the amp.

You'll generally find that most tweed era Fenders run less voltage on the input and other signal tubes --- compared to BF and SF era amps. Prolly this is one big reason for the "tweed tone" versus the BF or SF tone.

In any event, higher plate voltages on these 12AX7 and 12AT7 can lead to a shorter life. Plus, a tendency to become noisy. I'd run good PI and reverb driver tubes. In addition, a very quiet, tough input tube. And consider some voltage change, if the tone is too in-your-face, or strident sounding.


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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 11:48 am
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BMW2002Ti wrote:

You'll generally find that most tweed era Fenders run less voltage on the input and other signal tubes --- compared to BF and SF era amps. Prolly this is one big reason for the "tweed tone" versus the BF or SF tone.


So is that one of the reasons why BF/SF amps are brighter than tweed amps? Does higher plate voltage on the signal tubes = brighter tone? I'm asking cause that's what I noticed when I swapped rectifier tubes in my DR.


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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 12:40 pm
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Yes, brighter with a bit more headroom than the lower plate voltage tweeds. Since all Fender amps have their signal tubes cathode biased, you don't need to worry about idle bias (unless there is a big change in plate voltages --- like over 50VDC). But, the change in the plate voltages will shift the operating parameters onto another curve. Thus, the change in tone and response of the tube.


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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 2:09 pm
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BMW2002Ti wrote:
Thus, the change in tone and response of the tube.


This needs some qualification.

The location of the tone stacks between the tweeds and the blackface/silverface amps is more of a determining factor in the design's overall voicing. I'd stipulate that higher plate/anode voltages do play a role but IMO the positioning of the tone controls within the circuit layout is more significant. On the BF and SF amp, they're up front at the first gain stage but the earlier tweeds have them located further downstream, just ahead of the phase-inverter stage.

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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 9:46 pm
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Thank you both for the great info!

I checked the bias on the DR again tonight, with the Mullard 5AR4 in there... why would the plate voltage go up by 5 volts (470) and the bias by 2 mA (23)? Is this related to the power in the house? :?


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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 9:48 pm
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I would think so. It sounds like you have a pretty fresh 5AR4 there.

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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 9:59 pm
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It's a Sylvania branded Mullard rectifier, I think I got it about 3 years ago for the DRRI, which is now gone. The other BF amps I have came with their original Mullard rectifiers, so now it's just a spare.

Image

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Post subject: Re: Rolling tube rectifiers
Posted: Sun Jun 08, 2014 10:01 pm
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Guard that thing like your kid sister's virtue......it's a good one!

Arjay

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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 7:05 am
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I know, that's why I was making sure it's safe to test it in my SF amps, I'd hate to damage that tube!

I'm gonna borrow one of the other Mullard rectifiers I have in my BF amps and compare numbers...


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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 7:33 am
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cedarblues wrote:
I know, that's why I was making sure it's safe to test it in my SF amps, I'd hate to damage that tube!

I'm gonna borrow one of the other Mullard rectifiers I have in my BF amps and compare numbers...


Blackburn, Mullard made GZ34 (f32/33) are tough as nails. They'll pump out very good B+ for years and years --- as long as the PSU filter caps and resistor rail is healthy. And the first filter stage does not exceed a total of 40mfd.

The other rectifiers in this league are the big bottled Sylvania/Philips 5AR4 and the smaller GE 5AR4. I'm not quite sure why modern made rectifiers have a hard time meeting the old-time specs. In general, Chinese made "5AR4" met current specs but not the high B+ specs of NOS. And Russian made, the opposite: good B+, not as good current demands. I have not tested the new Gold Lion GZ34/5AR4.


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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 12:28 pm
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BMW2002Ti wrote:
In any event, higher plate voltages on these 12AX7 and 12AT7 can lead to a shorter life. Plus, a tendency to become noisy. I'd run good PI and reverb driver tubes. In addition, a very quiet, tough input tube.


You weren't lying about needing a good reverb driver! I noticed the reverb driver tube shield was very hot, so I removed it and noticed the Mullard CV4024 red plating! Never seen a preamp tube red plating before. The PI tube (same Mullard) was fine. Psvane tubes were in V1 and V2 and were also very hot.

The amp was working fine with the GZ34 in there and sounded very nice, it somehow got a little cleaner and brighter. But it kinda lost something this amp had, sweet highs full of harmonics... so I think I'll go back to the original rectifier.


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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 3:13 pm
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cedarblues wrote:
...so I think I'll go back to the original rectifier.


A wise decision, weed-hoppah.

:wink:

Arjay

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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 5:35 pm
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Retroverbial wrote:
A wise decision, weed-hoppah.

:wink:

Arjay


You should've told me not to bother after my first post :mrgreen:


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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 7:14 pm
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Long-term, it wasn't going to cause any harm. So I thought I'd allow you to......indulge yourself.

:mrgreen:

Arjay

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Post subject: Re: Rolling tube rectifiers
Posted: Mon Jun 09, 2014 9:12 pm
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LOL Thanks!


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