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FDP Forum / Fender Amps: Vintage (before 1985) / Vintage Rectifier Tubes?

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roadhog96

USA / CT.

Sep 11th, 2016 01:07 PM   Edit   Profile   Print Topic   Search Topic

Is it common practice to replace the GZ34 with a 5U4GB? I just bought a 67 SFPR with a 5U4GB.

Guitar Fool
Contributing Member
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Sunshine State

Just a pawn in someone else's game
Sep 11th, 2016 01:09 PM   Edit   Profile   Print Topic   Search Topic

my 64 deluxe uses a 5U4 instead of a GZ34....the power transformer has been replaced..so I can use 6l6 or 6v6 tubes...I'm guessing that's why the change

BbendFender
Contributing Member
*********

American Patriot

I'm on guard these days.
Sep 11th, 2016 02:16 PM   Edit   Profile   Print Topic   Search Topic

If you simply change rectifier tubes you may damage your amp. Voltages vary a great deal with different rectifier tubes. I'd recommend using that ones that are meant for your amp.

jazzguy
Contributing Member
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Philly, B-3 Capital

don't dream it be it
Sep 11th, 2016 03:21 PM   Edit   Profile   Print Topic   Search Topic

I believe PR's changed to 5u4gb's around this time


roadhog96

USA / CT.

Sep 11th, 2016 07:41 PM   Edit   Profile   Print Topic   Search Topic

This 68 Pro Rverb originally came with a GZ34 it was actually made in 67. The GZ34 rectifier tube was changed to a 5U4GB rectifier tube in 2013 as the amp tech thought this tube produced the most ideal B+.

I don't know if when the tech installed the 5U4GB if he changed anything else.

I want to put a GZ34 back in the way it came from the factory in 67. I want more clean headroom from this amp the 5U4GB does just the opposite.

Is there anything else I need to do if I change out the tube or can I simply swap tubes and check the Bias?

(This message was last edited by roadhog96 at 11:26 PM, Sep 11th, 2016)

jazzguy
Contributing Member
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Philly, B-3 Capital

don't dream it be it
Sep 12th, 2016 07:29 AM   Edit   Profile   Print Topic   Search Topic

most people that post PR mean Princeton Reverb.
that's what I was referring to.
you'll be fine putting a GZ-34 in your Pro Reverb

roadhog96

USA / CT.

Sep 13th, 2016 08:40 PM   Edit   Profile   Print Topic   Search Topic

Sorry about the confusion jazzguy, I guess I should have spelled Pro Reverb out, I see your point. Thanks for the good news, the GZ34 will be going back in as soon as it arrives.

New Amp on its way

(This message was last edited by roadhog96 at 10:51 PM, Sep 13th, 2016)

BbendFender
Contributing Member
*********

American Patriot

I'm on guard these days.
Sep 13th, 2016 09:05 PM   Edit   Profile   Print Topic   Search Topic

Dang, that amp is perfect.

roadhog96

USA / CT.

Sep 13th, 2016 09:28 PM   Edit   Profile   Print Topic   Search Topic

Yes it is, that's why I couldn't pass it up. I use to play one just like it years ago in a band and I miss it. This one is almost new like it's been in a time capsule. It's had the normal cap job and AC cord done a couple years ago. Other than the caps, cord, power and rec tubes it's original. This is the 349 one out if 500 manufactured in 67. All Blackface features with the 1st version SF grill cloth, blackline faceplate, snowman 8 knobs, Blackface circuit with blue molded tone caps and original transformers, etc. I'm psyched about this one, it's going to be my number one amp.

jazzguy
Contributing Member
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Philly, B-3 Capital

don't dream it be it
Sep 14th, 2016 08:39 AM   Edit   Profile   Print Topic   Search Topic

very tidy amp.
I bought 2 dead mint blackface Pro's from Gil Southworth eons ago. eventually sold them both because they sounded flubby.
it was probably the speakers.
I bet if you slap a couple of your vintage C12N's in there that amp'll sing Roadhog.


roadhog96

USA / CT.

Sep 14th, 2016 09:23 AM   Edit   Profile   Print Topic   Search Topic

jazzguy, that's exactly what I plan on doing. I have two that I'm not using right now. Those vintage C12n's sound great. Speakers can make or break a good amp sound for sure.

(This message was last edited by roadhog96 at 08:56 PM, Sep 14th, 2016)

blakef

USA

Sep 15th, 2016 08:17 AM   Edit   Profile   Print Topic   Search Topic

You can 'use' the voltage drops of different rectifiers to your advantage, as certain amps sound better with their circuits running a bit lower than was intended - the original Bassman is a good example where running a 5R4 instead of the specified rectifier really makes the amp sing.

The problem is that some rectifiers won't substitute because they draw too many amps (which your transformer might not handle) or can't take as much voltage as others - so you have to look at the values.

I have a compiled chart that assists in picking a different one to see if it sounds better:

Tube Type DC mA PIV FIL AMPS Max ACV DCV V DROP
5AR4 / GZ-34 250 1500 1.9 450 415 10
5V4-GA 175 1400 2 375 400 25
GZ37 350 1000 2.8 450 388 37
5U4-GA 250 1550 3 450 381 44
5U4-G 225 1550 3 450 381 44
5U4-GB 275 1550 3 450 375 50
5Y3-G/GA 125 1400 2 350 365 60
5R4GYB 250 3100 2 900 362 63
5R4G/GY/GYA 250 3100 2 750 358 67

As an example, going in a Bassman, the drop is 10VDC with the spec'd rectifier, but substituting a 5R4 drops 63-67 VDC making the entire circuit 'sag' and give the overdrive easier. The important thing to note is that the filament current and voltage handling is ok with this swap.


Steve Dallman
Contributing Member
**********

Merrill, Wisconsin

Age is just a number...mine is big
Sep 15th, 2016 09:37 AM   Edit   Profile   Print Topic   Search Topic

Fender changed to the 5U4 when the supply of GZ34's diminished. They made voltage changes to the power transformer to compensate for the greater voltage drop. They should not just be interchanged as the higher voltages from a GZ34 may exceed the voltage handling of the B+ filter caps.

If the B+ caps are in parallel, the voltage will likely be exceeded. Rewiring the power supply to use series caps (using values that will match the original capacitance) will allow using a GZ34 if you want the higher voltages and resulting headroom.

roadhog96

USA / CT.

Sep 22nd, 2016 11:50 AM   Edit   Profile   Print Topic   Search Topic

Amps been here for several days now and I updated the family photo. It's everything the seller said it was and then some. it's a keeper for sure. Can't believe how nice this amp sounds for an open back cab. Don't know if the Jensen C12NA speakers can improve the sound of this amp any but am looking forward to trying them out just to see. Also will be changing the Rec tube back to the GZ34.

68 SF Pro Reverb and New Family

(This message was last edited by roadhog96 at 02:25 PM, Sep 22nd, 2016)

urby
Contributing Member
*********

Seattle, Wa

Not quite my tempo
Sep 22nd, 2016 12:14 PM   Edit   Profile   Print Topic   Search Topic

Awesome pic!

Guitar Fool
Contributing Member
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Sunshine State

Just a pawn in someone else's game
Sep 22nd, 2016 06:08 PM   Edit   Profile   Print Topic   Search Topic

wow...nice looking amp for sure...

jeez.. I remember a few years back when people used to turn their noses up at the mention of Silver Face amps... not any more!

yeah and ditto on the C12N...good choice

SoK66

USA

We had the hit but Van got the money
Jan 8th, 2017 04:16 PM   Edit   Profile   Print Topic   Search Topic

Best practice is to use the GZ34 and reduce your line voltage to around 117vac using a buck transformer device, like The Amp Preserver, Browner, etc. When the amp was built 117 vac wall voltage was the norm. Today's line voltage will increase the internal operating voltage (B+) about 20 - 25 volts. Running it at 115 - 117 vac will bring all the internal voltages into line, with the best guide being the heater voltage.

Using a 5U4GB in a Fender amp originally spec'd with a GZ34 works fine. The primary issue is that the 5U4GB increases sag. It will also draws 50% more amperage (3 vs 2). This is really not a concern with Fender power transformers, they can handle the increased draw without any problem.

SoK66

USA

We had the hit but Van got the money
Jan 8th, 2017 04:16 PM   Edit   Profile   Print Topic   Search Topic

Best practice is to use the GZ34 and reduce your line voltage to around 117vac using a buck transformer device, like The Amp Preserver, Browner, etc. When the amp was built 117 vac wall voltage was the norm. Today's line voltage will increase the internal operating voltage (B+) about 20 - 25 volts. Running it at 115 - 117 vac will bring all the internal voltages into line, with the best guide being the heater voltage.

Using a 5U4GB in a Fender amp originally spec'd with a GZ34 works fine. The primary issue is that the 5U4GB increases sag. It will also draws 50% more amperage (3 vs 2). This is really not a concern with Fender power transformers, they can handle the increased draw without any problem.

SoK66

USA

We had the hit but Van got the money
Jan 8th, 2017 04:16 PM   Edit   Profile   Print Topic   Search Topic

Best practice is to use the GZ34 and reduce your line voltage to around 117vac using a buck transformer device, like The Amp Preserver, Browner, etc. When the amp was built 117 vac wall voltage was the norm. Today's line voltage will increase the internal operating voltage (B+) about 20 - 25 volts. Running it at 115 - 117 vac will bring all the internal voltages into line, with the best guide being the heater voltage.

Using a 5U4GB in a Fender amp originally spec'd with a GZ34 works fine. The primary issue is that the 5U4GB increases sag. It will also draws 50% more amperage (3 vs 2). This is really not a concern with Fender power transformers, they can handle the increased draw without any problem.

Guitar Fool
Contributing Member
**********
********

Sunshine State

Just a pawn in someone else's game
Jan 13th, 2017 01:51 PM   Edit   Profile   Print Topic   Search Topic

a triple post is a rarity...congrats...;-0

Next 20 Messages  

FDP Forum / Fender Amps: Vintage (before 1985) / Vintage Rectifier Tubes?




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