New AB673 deluxe reverb combo build

[aussietim]

I am getting the goodies together to build a Deluxe Reverb Combo
I have just about everything I need to build the chassis up
I am looking for a list of all the correct sized screws and fasteners I need to assemble this amp I have a TAD chassis
I do not know if being German made it is metric or true to the original American imperial sizing
I live in a metric country and do not know which imperial screws etc I need or if it matters
thanks Tim

[martin manning]

TAD's DR kit document https://www.tubeampdoctor.com/media/pdf ... -02-21.pdf shows the various screws, which you can find by searching the part numbers on their site. Looks like they are using US sizes 4-40, 6-32, 8-32, and 10-32, which are a number size and the number of threads per inch. Equivalent metric sizes would be:
4-40 = M3x 0.5
6-32 = M3.5x 0.6
8-32 = M4x 0.7
10-32 = M5x 0.8

[aussietim]

Thank you very much
Are there any mods worth doing during the build? I know that we all tend to want to put a heap of bells and whistles on our builds only to find that many are pretty useless when using the amp.
The last amp I built had switchable power tubes and a boost switch, both of which I found to be not all that useful when playing
The Mods I am considering are: the robrob Normal Channel Reverb Mod, the Trainwreck Type-2/Lar-Mar Master Volume and possibly the Add a Mid Tone Pot mod
Are these mods worthwhile? I do not want to fundamentally change the sound of the amp as the deluxe reverb sound is what I want, I will only do these mods if it is going to improve the functionality of the amp

[martin manning]

Are there any mods worth doing during the build? I know that we all tend to want to put a heap of bells and whistles on our builds only to find that many are pretty useless when using the amp. ...
I do not want to fundamentally change the sound of the amp as the deluxe reverb sound is what I want, I will only do these mods if it is going to improve the functionality of the amp.

I'd build it (mostly) as designed to start, keeping the channels separate (BTW the reverb on normal is a very old mod). It's already very busy in the chassis, so finding space for a PPIMV would be tricky, and unnecessary for a 20W amp, IMO. You can always mod it later if you want.
I recently built a DR with a similar goals, but improved the bias supply and revamped the ground scheme as detailed here: https://ampgarage.com/forum/viewtopic.php?f=8&t=34541

[sluckey]

I think a Marshall style bias circuit is worthwhile.

If you are fond of tremolo, you may be interested in the Trem-O-Nator. Very easy to put in an AB763 amp.

Neither of these mods will change the DR sound.

[Stevem]

All the mid pot does if implemented in the Fender way is to cut the mids.
They can get a little bit of mid boost if you keep the mid pot cranked and very much lower down the bass and treble.

This is not much of a sound issue in terms of the bass getting lowered because if you play the amp up at 5 or more with good tubes, speaker and filter caps you will to have the bass pot down to 3 to avoid having the amp fart out on fat chords or on the low E string.

The bad thing about backing down on the treble pot is that it effects gain / sensitivity levels a good amount.

I found out 35 years ago that if you are playing out with any amp and want the best touch and sensitivity you can get, and you have it up to 6 or more on the volume pot, then you want your tone stack set up as close as you can to having all the tone pots wide open!

This is way so many great players that don’t use stomp boxes use a amp that only has a volume and a tone pot.
These type circuits have a minimal sign loss, and all that tone pot can do is roll off the highs.

These types of amp set ups while they are a one trick Pony , play sound and feel great once you get it set for your needs.
The amount of bottom that the speaker outputs is a big part of this.

[martin manning]

I think a Marshall style bias circuit is worthwhile.

What's your reasoning here, Steve?

[sluckey]

I think a Marshall style bias circuit is worthwhile.

What's your reasoning here, Steve?

The Marshall two stage filter provides smoother DC than the stock DR circuit. And the bias voltage floats to max negative rather than zero if the pot wiper fails.

There are other ways to improve the stock DR bias supply, add another filter cap to the pot wiper and add a failsafe resistor, but I just prefer the Marshall circuit.

[martin manning]

The Marshall two stage filter provides smoother DC than the stock DR circuit. And the bias voltage floats to max negative rather than zero if the pot wiper fails.

It's the same as the bias circuit in the DR I built up, which runs off the bias tap and uses the 10k Fender pot. That voltage comes on with the main power like the Marshall circuit too.

[aussietim]

Thanks Guys
I am thinking pretty much stock standard
Thanks Martin for pointing me to your build, could you please post your layout and grounding scheme so I can blow it up and look at it more clearly
I will go ahead with the 2 channel reverb
Reading Robrobs site he recommends the Trainwreck Type-2/Lar-Mar Master Volume and states that it needs to be incorporated in the initial build which is why I was asking about its usefulness
Most of the other mods are able to be added later so I can worry about them later, the only other possibility is a dwell control on the reverb,
If I decide to add knobs I will get a custom faceplate
BTW how do you find the GA-SC64 it is pretty much at the top of my list of speakers for this build, would you use it again?

[martin manning]

Just click on the image and you will see an enlarged view.

Yes, I like the SC64 speaker, and would use it again.

The only difficulty with installing the KF Type 2 PPIMV on the AB763 eyelet board is with the power tube grid leads, which connect to the PI coupling caps from below. If you want to prepare for that, just bring the leads from the tube sockets up (instead of down) through the hole in the board and connect them on on the top side. If you are not interested in overdriving the phase inverter, I think I would place the MV at the PI input. Easier (1M single gang audio pot), and it won't disrupt the power stage feedback. Either way, I would wait to see if you really need it before messing with the panel layouts.

[romberg]

If you are fond of tremolo, you may be interested in the Trem-O-Nator. Very easy to put in an AB763 amp.

Oh! I've not seen that before. If I'm reading this correctly, I think this trem-O-Nator leaves the driver side of the tremelllo tube unused. Thus freeing it up for use as another gain stage or CF. An ab763 with four gain stages would be kinda a sick stealth high gain monster.

I'm just about to melt solder on my first fender type build. It is an ab763 driving a pair of 6l6gcs. My current plan is to mix both channels before the reverb send
https://robrobinette.com/AB763_Modifica ... Reverb_Mod, heavily modify the normal channel and PI using some dumble and marshall type changes https://ampgarage.com/forum/viewtopic.php?f=4&t=35308 and add a PPIVMV. My hotrod normal channel was going to be missing the CF driven tone stack. But now here is a free triode! This all might be a bridge too far using a stock type circuit board.

Does the trem-O-Nator's increased oscillation frequency range go both higher and lower than stock? The above page just mentions that the range is increased. A lower than stock frequency would be cool.

Mike

[sluckey]

The LFO low frequency is 2.7Hz on my Band Master. I don't recall the upper frequency. But the LFO output is pretty constant over the entire range.

[aussietim]

Hi Steve
Is the Marshall style bias circuit and the Phoenix the same thing?

[sluckey]

Hi Steve
Is the Marshall style bias circuit and the Phoenix the same thing?

yes