What to do with Magnavox 6v6 amp?

[nsmith01tx]

thanks Phil, that makes sense

[sluckey]

I would suggest connecting the power supply to the 305v source rather than the NFB loop.

[Phil_S]

Oops! My bad. I meant to hook to the B+, not negative feedback. Sorry for the mis-direct. I shouldn't have cut off the power supply section.

[Kagliostro]

A 6AV6 has a consumption of 300mA on heaters, a 12AX7 the same

no advantage to use a 6AV6 instead of a 12AX7 (OK may be each triode B+ consumprion is around 3mA, so a 12AX7 consumption will be 3mA highr than a 6AV6, but 3mA didn't seems a value that can give problems to the PT)

If you prefer to use a triode instead of a pentode, use the 12AX7 (at least this is what I'll do)

You can borrow a lot of one tube preamps to use with your power section









I like this one




This are only a small part of the circuit you can use at your choice

--

BTW. I don't understand the purpose of R6 (150K) that connects the cathode to 305v supply node in the original schematic of the power section But that may be part of the Paraphase PI (that I still didn't understand at 100%)

Franco

[nsmith01tx]

A 6AV6 has a consumption of 300mA on heaters, a 12AX7 the same

no advantage to use a 6AV6 instead of a 12AX7 (OK may be each triode B+ consumprion is around 3mA, so a 12AX7 consumption will be 3mA highr than a 6AV6, but 3mA didn't seems a value that can give problems to the PT)

If you prefer to use a triode instead of a pentode, use the 12AX7 (at least this is what I'll do)

You can borrow a lot of one tube preamps to use with your power section
...

BTW. I don't understand the purpose of R6 (150K) that connects the cathode to 305v supply node in the original schematic of the power section But that may be part of the Paraphase PI (that I still didn't understand at 100%)

Franco

Thanks Franco, this helps a lot!
BTW, do you think this two 6v6 amp will produce about 15 watts?

[Kagliostro]

BTW, do you think this two 6v6 amp will produce about 15 watts?

I think around that power, to know more about we must know the OT primary impedance

Franco

[sluckey]

BTW. I don't understand the purpose of R6 (150K) that connects the cathode to 305v supply node in the original schematic of the power section But that may be part of the Paraphase PI (that I still didn't understand at 100%)

Fixed bias.

[Kagliostro]

Ahem .... 305v + 150K ............ OK, I can understand, sounds odd to my knowlwdge, but I can understand

Thanks Steve

Franco

[sluckey]

Ahem .... 305v + 150K ............ OK, I can understand, sounds odd to my knowlwdge, but I can understand

Gotta look at the other part of the voltage divider too... 470Ω.

[Phil_S]

On the suggestion about the 6AV6 vs. 12AX7, I agree that there are many practical reasons for using a 12AX7 and it is probably the better choice. My thinking was that you can find an old stock RCA or other great tube for very cheap. It's not like current production 12AX7's cost that much. The expensive ones that many people think are better are all old stock, old production.

[nsmith01tx]

OK, here's a new version incorporating all of your input. I tried to simplify things as much as I could, both in the preamp & power supply sections.
Please let me know what you think.

164_BA-schematic_New_Preamp-24Mar17.jpg

[sluckey]

I think the circuit is about ready. One thing... put a resistor ( ≈1K to ≈10K) between the 305V source and the preamp filter cap.

Have you even tried the Magnavox power amp to see if it works? Insure it's working before you start adding/modifying. You should be able to plug a cd player, etc. into the input. Even a guitar, although it won't sound very loud without a preamp.

[Kagliostro]

I would like to know the reason for only one triode of preamp

with two triodes a TS can be used as the second triode recover the gain lost in the toneStack

Thanks

A single pentode will have a gain as two triodes and less heater consumption, this was the reason for my first council (and also because 5879 has a good sound)

Franco

[nsmith01tx]

I think that idea came from using the Champ as the basis for the preamp model - where the 1st triode provides the initial amplification & the 2nd triode acts as the Phase Inverter. In this case the PI is already provided by the existing 12AX7 (as I understand it).

If using both sides is beneficial then that's be great. I initially looked at lifting the preamp section of the 18watt Lite IIb circuit you provided, but it seems to me that each half of the first 12AX7 is acting as a preamp for one of the 2 inputs. To save space I'm only using one input jack, so it didn't seem necessary to use the 2nd half.

Is that not correct? How would I use that circuit with only one input jack?

The other reason is that I have several spare 12AX7's already, and no 5879's.

[Kagliostro]

I think that idea came from using the Champ as the basis for the preamp model - where the 1st triode provides the initial amplification & the 2nd triode acts as the Phase Inverter

The Champ is an SE amp, so no PI, the second triode of the 12ax7 acts as a gain stage

In the schematic you posted you must study with attention the signal path at the input jaks, one can't do the job of both .....

that circuit must use two input or one input and a DPDT switch

BTW, have you an ef86 ?

Franco