Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: sd8450 on April 20, 2021, 01:13:17 am
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Hi All,
I have a 1966 Fender Showman Head with a busted output transformer. I intend to have the OT rewound in near future hopefully.
Meantime I temporarily installed an Output transformer suitable for a Fender Vibrolux Reverb and intend to only use 2 pieces 6L6 as I know this is electronically safe. I attached this OT without adding holes to chassis by using a scrap aluminum bracket instead.
My question to the group: Is it possible to operate this amp using a quad of 6L6s without damaging the output tubes or the output transformer? I thought of this question because I had once a Seymour Duncan 8450 combo tube amp with a quad of EL84 power tubes and 50 watts output and the output transformer in this amp is small in comparison to the Fender Vibrolux Reverb transformer.
Thanks for any help on this question.
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With the same power tubes, an amp can be different output power depending on the voltages of B +, the desing of the preamps etc.
Which explains the different output transformer size.
Are you absolutely sure that your output transformer is defective?
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With the same power tubes, an amp can be different output power depending on the voltages of B +, the desing of the preamps etc.
Which explains the different output transformer size.
Are you absolutely sure that your output transformer is defective?
Thanks Latole! I am sure that the Showman OT is defective, and I found out later that it was already a rewound OT when I got the amp though it still has the original Fender laminates and OT casing. I have restored already a number of vintage Fender amps and this one took me a bit longer to repair because the OT appeared okay in continuity tests. Only after substituting with the Vibrolux Reverb OT I found out that it was the Showman OT that was causing the amp problem.
I asked the question because I want to know what is the effect of using a Vibrolux Reverb OT in a Fender Showman Amp and if a Quad of 6L6 can still be used.
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I asked the question because I want to know what is the effect of using a Vibrolux Reverb OT in a Fender Showman Amp and if a Quad of 6L6 can still be used.
I won't.
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I asked the question because I want to know what is the effect of using a Vibrolux Reverb OT in a Fender Showman Amp and if a Quad of 6L6 can still be used.
I won't.
Same here, this is a temporary solution. As I said in original post I know enough that it is okay when only two 6L6s are installed in the Fender Showman effectively reducing the output from 80 watts to 40 watts and using a 4 ohm speaker impedance.
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I have a 65 Showman. Just picked it up last year. Technically it’s a Dual Showman, 2k to 4 ohm OT. I don’t notice a huge difference in 40 watts vs 80 watts (2 vs 4 6L6). The low end breaks up a touch more but it’s nearly the same feel and volume. 4x6L6 just firms things up even more and let’s me push it way past what I actually need. I’d just run yours with 2x6L6 with the VR OT just to be safe. You don’t gain much tonal benefit in exchange for massively oversaturating your OT. I think the VR OT is rated at 30 watts.
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I have a 65 Showman. Just picked it up last year. Technically it’s a Dual Showman, 2k to 4 ohm OT. I don’t notice a huge difference in 40 watts vs 80 watts (2 vs 4 6L6). The low end breaks up a touch more but it’s nearly the same feel and volume. 4x6L6 just firms things up even more and let’s me push it way past what I actually need. I’d just run yours with 2x6L6 with the VR OT just to be safe. You don’t gain much tonal benefit in exchange for massively oversaturating your OT. I think the VR OT is rated at 30 watts.
Thanks Jordan86! Yes I agree and understand that 80 watts sound level is not twice as loud as 40 watts. It is just 3 dB more sound pressure level. There are some people nowadays who actually prefer less power and 35 or 40 watts is more than enough in most situations.
I am just curious to know if somebody has tried this or know for certain that no ill effects could happen if a Vibrolux Reverb transformer is used in a Fender Showman type of amp. I am just not brave enough to try this in actual as tubes and OT are quite expensive to replace.
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Theoretically you can use that OT with a quad of 6L6s, but since the primary impedance is halved, you should also half the secondary impedance, ie, a secondary marked 4Ω should be connected to a 2Ω speaker load.That will make everything happy as far as impedance matching is concerned. BUT (and this is a big but) 4x6L6s can pump out twice as much current as 2x6L6s. Your Vibrolux OT may not be able to handle that extra current and risks a burned out primary. I suggest you don't do this.
Instead, and particularly since this is a temporary condition while waiting for a correct OT, I suggest you simply remove two 6L6s. Your peace of mind will be happier.
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Theoretically you can use that OT with a quad of 6L6s, but since the primary impedance is halved, you should also half the secondary impedance, ie, a secondary marked 4Ω should be connected to a 2Ω speaker load. That will make everything happy as far as impedance matching is concerned. BUT (and this is a big but) 4x6L6s can pump out twice as much current as 2x6L6s. Your Vibrolux OT may not be able to handle that extra current and risks a burned out primary. I suggest you don't do this.
Instead, and particularly since this is a temporary condition while waiting for a correct OT, I suggest you simply remove two 6L6s. Your peace of mind will be happier.
Thank you very much Sir Sluckey! This is exactly the information I needed especially about the risk of burning out the primary of the OT. You also confirmed from what I am able to gather from other forums but was not so sure about that the speaker impedance required will then be 2 ohms in this case. I will never of course use or even try 4 6L6s when using the Vibrolux Reverb OT in this amp as per your advise. Thank you again!
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You only halve the impedance if running all 4x6L6. Which you should not do to begin with.
So run just 2x6L6 and match the load to the stock spec of the OT. If it’s 4K to 4 ohm, then connect to 4 ohm load with 2x6L6
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You only halve the impedance if running all 4x6L6. Which you should not do to begin with.
So run just 2x6L6 and match the load to the stock spec of the OT. If it’s 4K to 4 ohm, then connect to 4 ohm load with 2x6L6
Thank you Jordan86, I will run it using 2 x 6L6 and with the correct impedance match of 4 ohms for the speaker. Now it is very clear to me that trying to use 4 x 6L6s with the Vibrolux Reverb OT is just asking for trouble. Thank you again!