rainman
152 posts
Mar 04, 2015
8:59 AM
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I recently purchase a used Reissue and it has the Heyboer TO20 output transformer upgrade. It also has J/J 6V6S output tubes set to 23 Milliamps balanced bias. I love the amp and my only change was to change out V1 from 12AX7 to a nos 5751 which made a big difference. The 6V6S's have a later breakup than than other 6V6's but are maybe needed for the Heyboer. My question is would another 6V6 be a better choice for harp with this setup?
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Barley Nectar
696 posts
Mar 04, 2015
9:21 AM
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I have a couple of Princetons. One is a '76, one is a scratch build with Bassman iron, 35W. I have 6V6s in the "76 PR w/ a Deluxe OT. Your Hyboer upgrade probably gives more headroom and better base response. While other 6V6's will work fine with that OT, the JJ's are a good choice. Your amp will not have the compression of and original PR due to the larger OT. Some folks prefer the tone of traditional 6V6's which the JJ's are not. This is all personal preference. The only way you will know which tubes are better for you it to try them. Remember to rebias the amp when you install different power tubes...Good luck...BN
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HawkeyeKane
2732 posts
Mar 04, 2015
9:32 AM
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Important question for you rainman...do you know what year your PRRI was issued? And do you know if it has its original power transformer as well?
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Hawkeye Kane - Hipbone Sam
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Kingley
3849 posts
Mar 04, 2015
9:47 AM
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I'd say the JJ Tesla 6V6S are a good choice. If you like the sound with them than I wouldn't bother changing them.
I run my '65 Princeton Reverb Reissue completely stock. I didn't feel the need to change anything as in my opinion it's perfect for harmonica straight out of the box.
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rainman
153 posts
Mar 04, 2015
9:56 AM
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Thanks Barley, Hawkeye I don't know age can you tell from the serial number? Nothing change inside except the Heyboer Transformer. It also has a replaced plywood baffle and a Celestion G10 Alnico Gold Speaker. It sounds great, but thought if I could change out tube's a get a little earlier breakup it might be nice.
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rainman
154 posts
Mar 04, 2015
9:59 AM
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Kingley, Thanks for you response. Your insistence that this was a great harp amp did sway my decision. :)
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Kingley
3850 posts
Mar 04, 2015
10:14 AM
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Rainman - They really are great amps! :)
To get earlier breakup I'd suggest putting the 12AX7 back in V1, keep the treble around 1-3 and the bass up full. Then use either a Shure 545 or a good bullet mic into input 1. If I'm stood right next to it, I can easily get my Princeton up to 5 on the volume without feed back using a 12AX7. Which is pretty loud. If I move away from the amp then I can get the volume even higher. Other than that I'd look at mic cupping and playing technique. All those things combined should give you the dirtier sound you seek.
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Barley Nectar
698 posts
Mar 04, 2015
10:20 AM
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Your amp is set up for clean. Push those power tubes a little more(less negative bias) MIGHT give you earlier breakup. Might also promote feedback. Don't know if your PT will push that hard, those JJ's are stout! You could also try cold bias for more crunch. You can go as low as you want depending on the bias supply negative voltage capabilities. You could also return the amp back to stock. You could also put a switch on the NFB for more distortion. DO NOT drill holes in a Fender Chassis!!! I like um the way you have yours now but that is just me...BN
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HawkeyeKane
2733 posts
Mar 04, 2015
10:20 AM
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rainman
The reason I ask you about this has to do with re-biasing if you swap power tubes again. For the last few years, Fender has been manufacturing their amps with power transformers to meet international consumer standards in terms of fire safety. This means thermally sealing the power transformers so they don't heat up beyond a certain temperature. The problem with this is if you bias your tubes too hot, it'll short out the power transformer and you could be left needing not only a new PT, but also new power tubes, and potentially a new rectifier tube as well.
It'd all depend on exactly how old your PRRI really is of course. Just trying to save you any extra headaches...
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Hawkeye Kane - Hipbone Sam
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rainman
155 posts
Mar 04, 2015
10:55 AM
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Barley, I would say that is true that it's been setup for clean. Would Higher bios create earlier breakup ? Hawkeye I'll see if I can get an age on it. Thanks!
Last Edited by rainman on Mar 04, 2015 2:07 PM
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hvyj
2636 posts
Mar 04, 2015
12:56 PM
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FWIW, I have had positive results tubing down the phase inverter in my amps. To do this on a PRRI, put an ECC823 in V4. This tube is made by JJ and is a backwards 12DW7. It gives you a 12AU7 for the PI and keeps the vibrato driver a 12AX7.
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HawkeyeKane
2734 posts
Mar 04, 2015
1:12 PM
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"I think I run a AT7 in the PI of my Silverface PR. Is that the stock recommendation in a PR?"
AT7 should be your reverb driver Dave. Inverter on a PR is only a half of an AX7. Not sure which though...
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Hawkeye Kane - Hipbone Sam
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SuperBee
2443 posts
Mar 04, 2015
1:15 PM
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Yeah, I figured it out too long ago, now I just play it. It's all good whatever. My very favourite of my amps.
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Barley Nectar
699 posts
Mar 04, 2015
1:36 PM
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Rainman, Didn't say anything about higher voltage, although the B+ voltage will rise somewhat if you run the power tubes cold.
I suggest you study the effects of bias on tone in tube amps. Also suggest you study tube theory in general before you make any changes on that amp. Trying to follow web advise without knowledge will lead to a lot of wasted time and money...BN
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rainman
156 posts
Mar 04, 2015
2:10 PM
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Sorry Barley was editing post above and got interrupted. I think it's a great amp and will leave alone for now. I don't know how much time is on these tubes and thought I might buy a new set and wanted to make best choice. Thanks you all for the help.
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