Power Tranny Swap

[ajeffcote]

Hello to all of you.I am new to the forum and new to electronics in general.I do love playing the guitar and now I want to start taking care of and working on my amplifiers.Want to build one also,but that's about six months out.
Last year I bought a new Fender DRRI without even playing it.I used to play the old ones,had a '64 for a while,when I was a kid,and I do remember that they didn't sound like this new one.So I have decided to try to make my DRRI sound as good as it can.
Enter Mercury Magnetics.People have told me that with their replacement/upgrade transformers,proper tubes and bias and maybe a better speaker my DRRI will sound as good as or better than the vintage amps.
Being easily swayed when it comes to things that I consider to be fun,I bought new tubes,a bias tool,a new multi-meter,soldering iron and all four transformers for my amp.Tubes,output and reverb transformers,installed and rebiased,my amp definitely sounds better.
Installation of the output and reverb trannies went well,just swapped them out.And it looks to me that the choke will be just as simple.
The power tranny looks like there may be more involved than just R+R.Is this just a simple matter of taking the old one out and installing the new one?Any tips,advice,thoughts that might help a complete beginner would be most appreciated.
It might help if I voice my original complaint about this amp.It just sounds too harsh,and overly bright.I also removed the bright cap from the volume pot on the vibrato channel,which calmed it down a little.
Thanks in advance.Aubrey

[PRNDL]

The power tranny looks like there may be more involved than just R+R.Is this just a simple matter of taking the old one out and installing the new one?Any tips,advice,thoughts that might help a complete beginner would be most appreciated.
It might help if I voice my original complaint about this amp.It just sounds too harsh,and overly bright.I also removed the bright cap from the volume pot on the vibrato channel,which calmed it down a little.

Congrats --- you've learned a lot!!

Swapping the PT won't be too hard, although there are a lot more wires, which can be confusing.

[MWJB]

What B+ voltage do you get with the original PT? An original Blackface Deluxe should run <425vdc at the power tube plates with 30mA+ of plate current on the 6V6s...give or take.

Unless your voltages are significantly different (higher), there's not really going to be a lot of point in changing the PT.

[Bruce / Mission Amps]

I agree with MWJB.
The power tranny is not much of an issue with this amp but since you bought it, I'd still consider using it.
However, with respect to the 425vdc x 30ma comment, I have never found a stock black face Deluxe Reverb that ran it's power tubes at close to 13 watts unless someone set it that way. Don't get me wrong, they sound great at high power tube idle current but the amp will be a power transformer over heater and power tube eater.
8-10 watts each is safer cleaner and actually sounds more "classic" black face Fendery. So you have to decide which you want... longer term tube life and reliability or that underbiased
E. Johnson overdrive tone.

With respect to tonal changes in these amps, here a few easy mods...
Replace that speaker with something like a Celestion G12H30, MOJO BV30H, Eminence Red,White and Buues or WeberVST equiv.
Dump all the SOVTEK 12AX7WA tubes and use reissue Sovtek/Tung-Sol 12AX7s for the first two preamp tubes and or JJ ECC83s/12AX7s instead.
Find a NOS 12AT7 for the PI/driver and if you budget allows it, use NOS RCA 6V6s or at least JJ 6V6s.
Then rebias the power tubes so they are idling at around 8-10 watts each, (power tube idle current time plate voltage).
The power tranny does not have enough excess high voltage current to go much more then that ... and although a 5AR4 is correct, think about using a good old NOS 5U4GB rectifier tube to get some lower B+ voltages, which will soften the tone. This will require upping the idle current in the power tubes but keep them in that 8-10 watt range.
Yes, the 5U4GB does draw more filament current but I have not run into a bad PT yet using one in that amp.
If you feel like diving in more, use all polyester coupling caps like Mallory 150s. Illinois polyester axials, MOJO Dijon caps , Sozo or equiv boutique caps if you want... but not polypropylene caps like O'drops, Xicon MPPs or the like.
For small value pF caps I'd use silver mica or maybe polystyrene, but not ceramic and, reduce the amount of NFB in this amp by replacing the 820 ohm resistor with a 1500 ohm resistor.

Here is a link to an interesting read...
http://aga.rru.com/Events/MM-DRRI-rebuild/

[MWJB]

Sure, the choice is yours how much current you want to run the tubes at, take 30mA at 425 as a reference point. Modern 6V6s will handle higher plate voltages if you bias colder than this (more than 425v on the screens of many NOS types can be risky). The PT will take 30mA per tube comfortably.

[ajeffcote]

Power Tranny Swap

Thank you for your replys.I have just now gotten around to checking this post.Been rather busy lately.
The new tranny is in the amp.No problems at all on the install.But it is a bit stonger than the original.At the old bias setting the plate voltages went from around 420 to around 452.Tried to adjust the bias and with the pot maxed out it was still running cold,16.5ma @ 450V.With advice I received here I replaced the load resistor with a smaller value and now I have plenty of adjustment available.
Also put new tubes in.JJ's GZ34,ECC81's,ECC83's + 6V6S's.And one of the 83's is the gold pin model.I put it in the first slot on the vibrato circuit.All the new transformers are Mercury Magnetics.I put an Eminence Legend GB12 in also.It is not the same amp.The reverb was good but now it is outstanding,very smooth,no sproingyness(what a word!)The overall tone is much mellower,smoother but pick attack is sharp,punchy,precise.The bass was spongy and sloppy with the Eminence speaker before the changes.Not anymore.I am very pleased with the outcome.So far.
I plan on replacing all the cheapo caps that Fender cut costs with.And maybe changing some of those values while I'm at it just to experiment a little.
Thanks again,Aubrey

[ajeffcote]

Forgot to mention,I settled on 23ma at about 432-434V.
That extra 12-14V makes a difference in the sound.
The rectifier tube is glowing a little brighter than I remembered,but it doesn't look like it's near a meltdown.