roberts 770x mods?

BENDYmusic · Post by **BENDYmusic** » Thu Dec 08, 2005 12:57 pm

Wow thats awesome, I will certainly dig deeper into this. I am, however, unable to download the docs you posted, all I see is a blank page. Seems like it would be cool to have a selectable transformer in / out option, as well as impedance taps. Are you also using the tone control for anything? If you would be so kind as to post your schematics and notes again, I will be forever grateful.

RodC · Post by **RodC** » Thu Dec 08, 2005 2:50 pm

damn, http://www.beyondsanityproductions.com/ is showing up blank?

I hope I dont have probs with my provider.

Works OK here??

Powweb sucks, but if you need a lot of bandwith you cant beat their price.

RodC · Post by **RodC** » Wed Mar 01, 2006 7:56 pm

ubertar, I hope you have been working on your pres! LOL I just got my 2 pres in one mod working. I updated the zip file on my website with the schematic. I also made a note in the doc.

From the doc:

Other Mods I have tried

2 Preamps in one mod: I have tried to build 2 preamps out of one, one preamp consisted of the EF86 circuit and the other was the 2 stages of the 12AX7. This was nice and versital, you could still use all the stages even the power output, simply by using ?? jumpers between all the stages. The only problem I ran into was that the EF86 stage really didn?t have enough gain. **3/1/2006 Update: I found an input transformer that provides the gain/sound I have been looking for to complete this mod. I believe this is the best configuration. The EF86 stage sounds great with the input transformer, and I still like the 12AX7 without the transformer. I believe the 12AX7 in this setup will make a great instrument DI as well. (I used a transformer out of a Shure M67 mixer, I hate to rob from one to fix another, but I have some that are in pretty bad shape.) I?ll call this mod the 2 Preamps in one mod. There is a schematic available.

ubertar · Post by **ubertar** » Wed Mar 01, 2006 8:50 pm

pm'ed you.

Everybody's X · Post by **Everybody's X** » Sat Mar 11, 2006 10:07 pm

I finally pulled the pres from my old M-7 today, and spent about four hours cranking my les paul though it into a 4x12

man this thing sounds great as a guitar amp

do your mods leave it so I could still use it that way as well as a mic-pre?

RodC · Post by **RodC** » Sun Mar 12, 2006 8:26 am

Yes, I just pull the power tubes to save them If I dont use the power section. The sound you are getting now will be virtualy unchanged.

You will end up with one extra pre with more options of gain and they will be cleaner sounding because of all the extra components that are removed.

WarrGo · Post by **WarrGo** » Fri Oct 09, 2009 3:58 pm

I know that this is an old post. But I have a Roberts 778x and an Akai 345. Can these be moded like the ones that you show here? I am pretty sure that the Akai 345 is a tube model bc it's a hernia waiting to happen.

newfuturevintage · Post by **newfuturevintage** » Fri Oct 09, 2009 4:41 pm

seeing this thread reminded me that I wanted to sell my m7, so it's up in the buy sell trade section here:
http://messageboard.tapeop.com/viewtopic.php?t=67296

RWood · Post by **RWood** » Sat Oct 10, 2009 12:33 am

WarrGo wrote: But I have a Roberts 778x and an Akai 345. Can these be moded like the ones that you show here?

Check the tube lineup in the Roberts 778x; I think that is the reel + 8 track version of the 770 and 771 which has similar amps to the Akai M6, M7, M8 models that Rod has documented so well.

The tubes in each of the two amps are: 6267 (EF86), 12AD7 (similar to 12AX7), 6BQ5 (EL84) and 6X4. Then one of the two amps will have a 6AR5 recording oscillator, which is not used in these mods.

I am not familiar with the Akai 345. Let us know what the tube compliment is.

RWood

RodC · Post by **RodC** » Sat Oct 10, 2009 6:16 am

WarrGo wrote:I know that this is an old post. But I have a Roberts 778x and an Akai 345. Can these be moded like the ones that you show here? I am pretty sure that the Akai 345 is a tube model bc it's a hernia waiting to happen.

I think the 778x is a Solid state unit.

From the size of the 345 it is prob one of the early solid state units as well.

WarrGo · Post by **WarrGo** » Sat Oct 10, 2009 7:12 pm

OK I just looked in the back of the recorders. The 778X does appear to be solid state. The 345 seems to be a hybrid. I see 4 power transisters on the back and at least 9 small maybe dual triodes inside. The only one that I could read a number on is a 12at7.

RodC · Post by **RodC** » Sun Oct 11, 2009 7:04 am

WarrGo wrote:OK I just looked in the back of the recorders. The 778X does appear to be solid state. The 345 seems to be a hybrid. I see 4 power transisters on the back and at least 9 small maybe dual triodes inside. The only one that I could read a number on is a 12at7.

That does seem like an odd ball. Maybe just the power amp is transistor.

Finding out what tubes are in there will shed more light.

dubold · Post by **dubold** » Mon Oct 12, 2009 10:39 am

RodC wrote:
WarrGo wrote:OK I just looked in the back of the recorders. The 778X does appear to be solid state. The 345 seems to be a hybrid. I see 4 power transisters on the back and at least 9 small maybe dual triodes inside. The only one that I could read a number on is a 12at7.
That does seem like an odd ball. Maybe just the power amp is transistor.

Finding out what tubes are in there will shed more light.

hey rod, was just thinking of you today. sent you an email in fact.

WarrGo · Post by **WarrGo** » Wed Oct 14, 2009 7:05 am

I am going to attempt to post some photos of the akai 345. Sorry not to get this done sooner but I went to see U2 Monday.

The tubes in this are.
back row R to L, 12AD7, 12AD7, 12AT7, 12AU7
front row R to L 12AX7, 12AD7, 12AT7, 12AU7
the tube to the far left is a 12AT7.

I think that the 12AX7 isn't original.

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roberts 770x mods?

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