5F11 Vibrolux with 6L6 tubes

gkaada

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Does anyone here use 6L6 tubes in their 5F11 Vibrolux clone?

I would be interested in their experience.

Will the tremolo still work with 6L6's?

Thanks,
 

gkaada

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I have a pair of PT/OT from an old 50W Ampeg SuperJet SJ12R (which used 6L6 tubes).
PT 94-270-30
OT 94-268-01

Would it be possible to use these transformers for a 5F11 build with 6L6 tubes?
I don't have the specifications for these transformers, only the schematic for the SuperJet SJ12R.

The PT has no 5v tap, so the rectifier has to be solid state or an SS adaptor.

Will I need to change or add any components to the 5F11 circuit?
I believe the target B+ voltage for 5F11 is 340V?

Thank you for advice,
 

gkaada

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Here are the schematics...
 

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  • Fender_vibrolux_5f11_schem.pdf
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  • ampeg_j12t_jet_ri.pdf
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NTC

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That Ampeg has EL84 output tubes, not 6L6'S. The OT should work with 6V6's, and the voltage should be about 6G2 correct (a 5F11 Vibrolux and a 6G2 Princeton have virtually the same circuit). These transformers are probably WAY under spec for 6L6'S
 

NTC

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Some things to consider for a "5F11" with 6L6's. These are based on my own "5F11" that can comfortable run two 6V6's with a 5Y3 rectifier or two 6L6's with a 5AR4 rectifier without rebiasing.

1. The speaker makes a HUGE difference. If you are going to use two 6L6's, you are going to get probably 30 to 40 watts of output. If you like vintage style speakers, you will probably need two. Otherwise you want one speaker with a high power rating.
2. You need transformers that can handle driving 6L6's. I built my 5F11 circuit in a tweed Deluxe Chassis. I went for a power transformer that can fit in the standard chassis cutout. I am currently using a Hammond 290BX. I have about 426 volts on the plates of the 6L6's. At idle, the whole am is using about 95mA. The transformer is rated at 138 mA, so it is going to run out of gas earlier than, say, a Vibrolux Reverb.
3. The OT needs to handle the output tube bias current as well as the higher current needed during operation. I am using an designed OT for a Vibrolux Reverb/Pro Reverb/Bandmaster etc. It is larger than a Deluxe Reverb OT. It is around 4K:4 ohms, so it is about 8K:8 ohms with one 8 ohm speaker.
4. My voltages are high throughout the preamp as well since I basically used all stock 5F11 values. This was a VERY clean amp until I doubled the feedback resistor value. In 6V6 mode, it starts to break up at about 4 (out of 12) and gets smoothly crunchy, not as ratty as a 5E3. WIth 6L6's, it still stays really clean up until about 9.
5. If you want to use 6L6's, there is no point in keeping the plate voltage low. You can if you want, but if you want 320V B+, just stay with 6V6's.
6. DOn't use a 5Y3 with 6L6's. They can't supply enough current unless you NEVER turn the volume up.
7. Don't do what I did - I followed the schematic completely. You should add 470 ohm, 1W or higher screen resistors. One of these days I will add them.


THe Trem works well with the 6L6's. They could probably stand to be biased a bit colder. They come in at about 70% and the 6V6's come in at about 67% PD. It does sound better with the 6V6's. The amp does not seem much louder with the 6L6's, though it does have a clearer sound. That could just be due to the pairs of tubes I have in the amp.

I made this amp about 15 years ago and then did some work on it last year (pt change) and again this year (feedback change). I really should do a proper writeup thread on this (one other person has asked). It is a weird beast and I have made some probably odd decisions due to trying to force a desired response from a specific speaker. I still do not consider this amp "done" after 15 years. I have never heard or played a real or vintage spec 5F11 or Harvard, but I doubt that mine sounds similar -it will have more bass and stay tighter much farther up the volume dial. It has a really nice percussive sound with my strats. It mostly gets used at low volume, so I have the 6L6's in there with an 8 ohm load. I CAN'T turn that up or the speaker will blow.
 

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  • vibrolux_5f11_schem_markup 2 6L6.pdf
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  • vibrolux_5f11_schem_markup1.pdf
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NTC

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One other thing to note - compare the 5F11 schematic's output section to a 5E7 Bandmaster, 5E6 Bassman, 5E4 or 5F4 Super, or a 5E5A Pro. component value wise, the output sections all look similar. The real difference is in B+ and the transformers. And the rectifier tube - can't forget that.
 

Lowerleftcoast

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The SJ12R schematic provided is not the 50W 6L6 version.

The 6L6 version shows a B+ of 400V.

The SJ12R has a SS bridge rectifier. If you want a tube rectifier, a EZ81 is rated to 150mA but it will cost 1A to power the filament. IDK the capability of the filament secondary of the SJ12R. The EZ81 will drop the B+ maybe 35 to 40V.

All in all, this transformer set could be used for 6L6 version. Just be mindful of the filament current draw. (Make sure you can touch the PT with your hand once everything is warmed up.)
 

gkaada

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Thank you for the comments,

Damn, I see that I uploaded the wrong file, sorry for that.
Here is the correct schematic for the Ampeg.
I also mixed up the models, there was a version with tremolo only (SJ-12R), and then the version that I had (SJ-12T) with both tremolo and reverb. My amp used 6L6, but I believe there were even some of these amps that came with EL34s, and obviously, the J-12T that used EL84s.

According to this schematic, I should expect a B+ of 400V with this 94-270-30 PT through a SS bridge rectifier. I believe that is OK for using 6L6 tubes, but I don't know the specifications for this PT and the current rating. Does anyone know who made these transformers?

B+ of 400V is 60V more than specified on the 5F11 schematic. How can I compensate for that in the circuit so that the amp will be usable? I hope I am not making something that I will never be happy with. I like clean amps but they need to be harmonic :).

A 5F11 (6V6) circuit that I built a couple of years ago has a 100K potmeter instead of a fixed feedback resistor. I did not use this pot much, just left it at approx stock value and thought the amp sounded best then. Uploaded a layout drawing for this 5F11 circuit.

I will check the schematics for the 5E4, 5E5A, 5E6, 5E7 and 5F4, and compare the components in the output section, and come back with suggestions/questions :)

Thanks,
 

Attachments

  • 27711H4_.pdf
    137.4 KB · Views: 8
  • AmpegSj12TUsersManual508673.1081832288.pdf
    965.3 KB · Views: 9
  • 5f11_Guitar_Amp_Odin_r1.pdf
    120.9 KB · Views: 6




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