Blackface to Silverface conversion for Twin Reverb?

Tyler Macy · Post by **Tyler Macy** » 27 May 2001 11:43 pm

No, it is not a typo. I have a 1969 twin that has been blackfaced (or mostly came that way), and I am considering converting it to 100 watt silverface specs for cleaner sound at high volumes. What do y'all think about this idea? How much tone would I be giving up for the added headroom? BTW, the amp has original JBL D-120Fs in it.

Thanks
Tyler

Ken Fox · Post by **Ken Fox** » 28 May 2001 8:24 am

I'm not sure how to answer all your questions on this. Is your amp tha 85 watt or 100 watt model? The Silverface coupling cap to the inverter is a .1 mfd as opposed to a .01 in the Blackface amps. You'll get some increase in the low frequencies. A lot of guys prefer to the leave the reverb section at Silverface specs. It's a better sounding reverb setup (from what I've read,anyway). The reverb tube is driven much hotter on the Silverface amps! There are some suttle changes in the inverter tube section as well. A good discussion on this can be found on Andy Ruhl's, Machine Gun Amps site. There's also a lot of ongoing discussion on the Fender Forum as well. http://www.users.qwest.net/~aruhl/mga/

Hamilton Barnard · Post by **Hamilton Barnard** » 28 May 2001 1:46 pm

Tyler, I don't see how converting a blackface amp to silverface specs is going to get you an once more of headroom -- as we are only dealing with the bias circuit and some 2000pF grid caps.

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Tyler Macy · Post by **Tyler Macy** » 28 May 2001 2:21 pm

How can conversion from 85 watts to 100 watts not give more headroom? The silverface twins I have played (all pre-master volume) stayed pretty much clean at essentially max volume. Mine starts to break up at around 4-5, giving overdrive at 5-6 and beyond. Don't get me wrong, it sounds great, but I think I may want it to be cleaner. However, i don't want to sacrifice much/any clean tone. Does anyone know of any modification that will allow this, perhaps not going all the way back to silverface specs, but something that will keep the amp cleaner?

Thanks

Tyler

Hamilton Barnard · Post by **Hamilton Barnard** » 28 May 2001 9:18 pm

A Twin should not go into overdrive on '5'; there's something that's not up to specs in that amp -- I'd have it serviced by a good tech.

Going from 85 watts to 100 watts is not even a 2db gain; a difference that would barely be heard.

Tyler Macy · Post by **Tyler Macy** » 28 May 2001 9:31 pm

Perhaps I mispoke by saying the amp "overdrives" at 5. It is not a fuzzy distortion at that level, but it is definitely clipping, and not the spanky clean sound I want. BTW, I am talking about 6-string through the amp for this discussion. I haven't used the amp for steel with the band yet.

Don't get me wrong, the amp is loud before it distorts- I just hear SF twins that stay clean forever. I know increasing from 85 to 100 watts won't increase max SPL very much, but won't it audibly increase headroom before clipping?

Thanks

Tyler

David Rich · Post by **David Rich** » 29 May 2001 5:41 am

One of the reasons the later silverfaces have more headroom is the higher plate voltages on the output tubes.

I may be wrong, but I don't think the 69 twins had the higher voltages yet.

Dave Rich

Bill Terry · Post by **Bill Terry** » 29 May 2001 6:55 am

I have a '69 that has been blackfaced and mine doesn't really distort at all until it's really cranked, around 7 or higher on the channel volume, and at that setting the volume is 'uncomfortably loud'. BTW, I checked every circuit voltage called out in the AB763 (BF) schematic and my amp had exactly the same measured values, (after the BF mod that is, because one change is the dropping resistor values on the power supply).

I'd agree something is not totally 'right' with your amp, although 'right' is a relative term since you're using it for guitar now and like it.

Also, there was a thread a while back about different pre-amp driver tube options, search on 12AX7 or something similar and you'll probably find it.

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Patrick Smith · Post by **Patrick Smith** » 29 May 2001 11:24 am

One thing I did recently, which I posted here, was to run the normal channel through the reverb circuit...now it's a usable channel with reverb/tremelo.

From there I changed out the values of the bass and mid pots, changed the values of the caps in the tone stack, changed the slope resistor value, and change the 120pF bright cap to a mica 47pF on the switch and another 47pF mica cap on the pot....All of these changes are basically making the normal channel like a 50's tweed twin. I don't have the words to describe how cool this now sounds! The other channel is now a joke in comparison.

My reason for mentioning it here, is that not only is the tone of that channel MUCH better than the regular twin reverb channel, now you actually have real midrange and not that scooped out sound, BUT, these changes made this channel at least twice as loud as the regular twin reverb channel...so if you want, LOUD, CLEAN HEADROOM, WARM, BALSY TONE you might want to do this simple conversion.

Major difference!

PMS

PS-oh yeah, I forgot, I ripped out all that master volume and boost nonsense...that also makes a difference