Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: string bender on November 30, 2022, 10:05:57 am
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I usually lend a traveling musician from the other coast to use a spare guitar and amp, a new re-issue Fender deluxe reverb. Thanks to him he broke in the speaker but this years tour of the band he plays in he show's up with the real deal, a 1965 Fender Deluxe reverb, recently gone over by an amp tech.
The difference in tone was noticeably better. SO, what is the reason. I was thinking today, possibly I could just start looking at replacing some of the hardware with vintage parts? Transformers came into mind. I'd like to hear from the many amp builders and their thoughts. Kind regards, Doug
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Sorry, but I have to ask - define "better"?
Ed
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The speaker and cab form perhaps at least 50% of of any rig’s tone.
Combo users especially seem to overlook this.
Try plugging amp A into cab B, and visa versa, and compare.
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My first thought would be the Schumacher output transformer in the original.
But it could be multiple cost saving differences in the reissue.
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Speakers. Cabs. Transformers. Everything matters, of course. :wink:
On the subject of transformers - somebody remind me, were AC line voltages significantly lower in 1965 than they are now?
OK - I just answered my own question. Fender's original 65 DR tube chart (US) shows 117 volts.
From another project that I'm involved with, it appears that 125 volts and higher is not uncommon where I live.
Is that enough to make a noticeable difference with an original 65 DR?
Has Fender adjusted their transformer spec's to account for today's line voltages?
Ed
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I've read that these are popular, especially in studios using vintage amps:
https://www.brownbox.rocks/products
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It’s worth noting that the vintage DR was recently serviced.
Perhaps it’s just working right / has a reasonable bias setting, whereas the RI may benefit from a tweak / good valves etc.
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I am a big fan of spreadsheets where i can enter _all_ voltages and it then calculates the various currents in the amp.
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I've read that these are popular, especially in studios using vintage amps:
https://www.brownbox.rocks/products (https://www.brownbox.rocks/products)
A person could build a couple of Sluckey's "Little Buckaroos" and still take a trip to Vail or Aspen skiing for that price!
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I usually lend a traveling musician from the other coast to use a spare guitar and amp, a new re-issue Fender deluxe reverb. Thanks to him he broke in the speaker but this years tour of the band he plays in he show's up with the real deal, a 1965 Fender Deluxe reverb, recently gone over by an amp tech.
The difference in tone was noticeably better. SO, what is the reason. I was thinking today, possibly I could just start looking at replacing some of the hardware with vintage parts? Transformers came into mind. I'd like to hear from the many amp builders and their thoughts. Kind regards, Doug
Did you check to see how hot the bias was?
But agree with what others said out the Schumacher OT and speaker (and tubes - of course)
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A person could build a couple of Sluckey's "Little Buckaroos" and still take a trip to Vail or Aspen skiing for that price!
And for an extra $20 you can add a volt/current meter...
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My original question (define "better"?) hasn't been answered yet. I hope we're enjoying our time going down the rabbit holes. :smiley:
FWIW, Fender's online material here in the US shows (or assumes) Line Voltage being 120V. Up 3 volts from 1965. Woo hoo!
Ed
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On the subject of transformers - somebody remind me, were AC line voltages significantly lower in 1965 than they are now?
OK - I just answered my own question. Fender's original 65 DR tube chart (US) shows 117 volts.
From another project that I'm involved with, it appears that 125 volts and higher is not uncommon where I live.
Is that enough to make a noticeable difference with an original 65 DR?
I used to own a 1964 Deluxe Reverb. It delivered 6.3vac on the heater winding when fed 120vac on the PT primary. No matter what the tube chart says, The 125P23B power transformer was designed to receive 120vac.
The 125P17A power transformer in my 1962 Deluxe delivers proper output voltages when fed 117vac.
So with the exception of the Champ/Vibro Champ, it seems the blackface amps were geared for 120vac outlet voltage.
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My original question (define "better"?) hasn't been answered yet. I hope we're enjoying our time going down the rabbit holes.
Here you go...
https://www.google.com/search?q=better+definition&oq=better+definition&aqs=edge..69i57j0i512l2j0i22i30l3j0i390l2j69i64.14827j0j1&sourceid=chrome&ie=UTF-8
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I used to own a 1964 Deluxe Reverb. It delivered 6.3vac on the heater winding when fed 120vac on the PT primary. No matter what the tube chart says, The 125P23B power transformer was designed to receive 120vac.
Did you happen to record the plate voltage? I'm just curious which currently available PT is actually closest to a real 125P23B.
The MojoTone 125P23B clone is 354-0-354, the Mercury Magnetics is 350-0-350, the Hammond is 330-0-330, the Pacific Audio is 330-0-330, and now defunct Classic Tone was also 330-0-330.
Thanks.
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Winding voltage is dependent on the current being drawn. Are those voltages at no load, full load (if so, what), or some point in between?
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I have a 1964 deluxe reverb. I could measure some voltages if you're curious what the ratios are
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Winding voltage is dependent on the current being drawn. Are those voltages at no load, full load (if so, what), or some point in between?
Thanks pdf64. But, certainly today we know the load of an AB763 with two 6V6's. If we know the typical plate voltages of a pre-CBS DR, we can contact the manufacturers and ask them if their specs are under load or not. Hammond states 330-0-330 with a 138mA load. That would be ~429VDC with a GZ34 under that specified load.
I know it doesn't really matter. JJ 6V6GT's will survive over a wide range of voltages. But, if we know the load of an AB763 and the plate voltage with 120VAC, we should be able to guesstimate which current production PT's are closest to an original 125P23B. Again, it doesn't matter too much. Like you said, speaker and cabinet play a bigger part than +/- 25VDC on the plates.
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Did you happen to record the plate voltage? I'm just curious which currently available PT is actually closest to a real 125P23B.
With 120vac input, I got 334-0-334v at the PT high voltage winding, 6.3vac on the filament string, 394vdc at the 6V6 plates when drawing 24.9mA of plate current per output tube. This was while using a (real British) Mullard GZ34.
... I'm just curious which currently available PT is actually closest to a real 125P23B.
The MojoTone 125P23B clone is 354-0-354, the Mercury Magnetics is 350-0-350, the Hammond is 330-0-330, the Pacific Audio is 330-0-330, and now defunct Classic Tone was also 330-0-330.
Go as low as you can. I never saw anyone here complain their B+ voltage was lower than they wanted, but I have seen plenty complain their B+ was higher than expected. I suspect that is due to lower winding resistance in modern PT clones.
But also know Fender didn't stay static with the PT and its ratings:
- The brown 6G3 Deluxe had 3 different power transformers, with 3 different B+ voltages.
- The blackface Deluxe had at least 2 or 3 different power transformers with different voltages.
- An owner of a 1965 Deluxe Reverb had a 125P23C power transformer that delivered 348-0-348v when fed about 121vac, 442v at the first filter cap, and 423vdc at the 6V6 plates when drawing 19.9 - 20.2mA.
- In 1966 Fender switched from "125P__" part numbers to 6-digit part numbers. Voltages could have changed after that switch.
- Sometime in the silverface years (likely early 1970s) Fender part numbers added a letter in front of the 6-digit part number.
- Fender generally kept part numbers unchanged after moving to the 6-digit part numbers, but anecdotal evidence suggests voltages may have moved around over time.
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I know the discussion has moved to a voltage focus. And I would never claim that voltage doesn't affect tone. But thinking on the original question as different tone rather than better. The capacitors, resistors, wire, cabinets, speaker are all different, and are all different age. One should not expect them to sound the same. But if there is a dramatic difference, I would suspect a problem. I help a friend with his DR reissue. It has had multiple issues with cracked PC board traces. Typically the amp does not fail, but the sound degrades.
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Fuse size is really related to the current draw of the amp that's plugged in. I "think" I have a 5 amp fuse in mine.
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… we know the load of an AB763 with two 6V6's.
What is it, eg under the conditions of idle, max clean output, and fully overdriven?
If we know the typical plate voltages of a pre-CBS DR, we can contact the manufacturers and ask them if their specs are under load or not. Hammond states 330-0-330 with a 138mA load. That would be ~429VDC with a GZ34 under that specified load.
How has the 429V been determined there?
Bear in mind that the winding voltage will rise from 660V as the loading decreases, to 702V with 0 current being drawn. https://www.hammfg.com/files/parts : :icon_biggrin:icon_biggrin:/pdf/290BEX :icon_biggrin: :laugh: :laugh:.pdf
I think the 660 to 702V should be a fairly straight line.
But the relationship between I AC and I DC is somewhat complex, as is the relationship between V AC rms and V DC.
I need to learn how to use Duncan’s PS2 app :laugh:
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I would think that you wouldn’t want to run an amp that has a mains fuse any higher than the bucking transformer 3A rating.
I totally agree. All the amps I have that would ever be used with the bucker use 2 amp or less line fuse.
If you want to run a bigger amp you need a bigger bucking transformer.
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> wouldn’t it risk burning up the bucking transformer (3A rating) to have a 5A fuse installed?
Assuming a perfect resistive load, the primary can be 3.3 Amps. See attached.
Small transformers can have surprisingly large reactive current. (Insufficient inductance.) Sometimes as much as the nominal resistive current. Agree to round-up generously.
If a transformer is bad or shorted the current will go to 15, 20, or more amps. It is unlikely to be just between 3A and 5A. It could be, yes. But also as an experienced transformer burner (even at shows), IMHO a 12V 3A lump is not an exciting fire.