SVT Bias and balance setting

[pbman1953]

K1 and common are 72 using the vr 1 bias control




k1 and k2 are now at 0, using the vr2 bias control, just at Ampeg wanted.

[sluckey]

Then, with power OFF, trim VR3 for 4Kohms +/-1Kohms. Done. Have a beer.

Probably the easiest way to do this is to pull V1. Now connect one meter probe to chassis and the other to pin 3 of the V1 socket. Adjust VR3 until your ohm meter reads 15K. Done. Have a beer.

[pbman1953]

Then, with power OFF, trim VR3 for 4Kohms +/-1Kohms. Done. Have a beer.

Probably the easiest way to do this is to pull V1. Now connect one meter probe to chassis and the other to pin 3 of the V1 socket. Adjust VR3 until your ohm meter reads 15K. Done. Have a beer.

I set it before I put the amp back together

[pbman1953]

Any tips to lubing the fan to get it to be quieter? It has the stock fan


Thanks

[PRR]

Is it squealing? Or air-noise? Cleaning the dust-scum for smoother airflow may reduce fan noise.

BUT a properly played SVT should leave no room for comments about its fan.

[pbman1953]

The fan exterior is clean. I'd a little lube and it should be fine.


Otherwise a new one is $35 from Fliptops. I'd guess a good desktop case fan would be good too

[PRR]

Is it 12VDC? Or 120VAC?

Low-price DC fans hide the bushing under the label, maybe a rubber plug under the label.

Good AC fans come all different ways.
__________________
https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/50093-

[pbman1953]

After watching some SVT videos, I want to replace the screen ,22ohm resistors. Viewing them again, they did look brownish and un-healthy looking. Before, one was bad and I should if replaced them all, now I'll go back and do it.


The question is , since the schematic says nothing, what value are the diodes they are connected with?




Thanks

[sluckey]

Many diodes have the numbers printed on the body of the diode.

[pbman1953]

Many diodes have the numbers printed on the body of the diode.

does 555- 2 with a sides "S" mean anything?


I have some IN4007-  r-SI, 1000v, 1A diodes

[sluckey]

Part numbers are on the schematic. According to this B15S parts list those 530555 diodes are rated 1000V_piv and 1 AMP. A common 1N4007 has those exact same parameters.

[pbman1953]

Part numbers are on the schematic. According to this B15S parts list those 530555 diodes are rated 1000V_piv and 1 AMP. A common 1N4007 has those exact same parameters.

Thanks!

edit... fixed quote... sluckey

[pbman1953]

Is 2 watt overkill for screen resistors? Is it OK to sub a 20 ohm instead of a 22?

[sluckey]

I'm at the parts shop and they have 15 ohm 5watt not 10 ohm. Still use?

I don't see any 10Ω resistors on the schematic.

[pbman1953]

I don't see any 10Ω resistors on the schematic.
[/quote




Going from 5 to 10.

[pbman1953]

They had the 22 in 1/2 watt

[sluckey]

I suggest using the correct parts.

[PRR]

2W 22r is 0.3 Amps. Screens have no business sucking that hard long enough to toast a big resistor. Either it is just old brown/oxidized varnish, or something is wrong.

And that is 0.3A *reverse* (since the diode bypasses normal screen current).

I have my own opinion (somebody over-designed) but certainly the stock factory values should work smokelessly.

What is a "parts store"? Like NAPA to get a tie-rod for the Jeep? DigiKey will sell any likely resistor, no compromise.

[pbman1953]

2W 22r is 0.3 Amps. Screens have no business sucking that hard long enough to toast a big resistor. Either it is just old brown/oxidized varnish, or something is wrong.

And that is 0.3A *reverse* (since the diode bypasses normal screen current).

I have my own opinion (somebody over-designed) but certainly the stock factory values should work smokelessly.

What is a "parts store"? Like NAPA to get a tie-rod for the Jeep? DigiKey will sell any likely resistor, no compromise.

Cool, I'll go stock. The part store is You Do It Electronics and has been in business for over 40 years. They have a parts floor and a audio video floor.


They stock NTE resistors in a large range of values

[sluckey]

They stock NTE resistors in a large range of values

Just not the values you need!   

[pbman1953]

They stock NTE resistors in a large range of values

Just not the values you need!   
[/quot


Actually they checked reserve stock and I lucked out

[sluckey]

You need some practice with the quote button!

[pbman1953]

Well, I finished  the  amp yesterday and it  was quiet and awesome. I turned it on today and there's no sound and loud hum.


What do I do first?

[pbman1953]

I found the hum. The positive signal wire fell off the square pre-amp plug.


A video I watched said that they are tricky and sometimes some tech's remake them.

[Latole]

Cool, I'll go stock. The part store is You Do It Electronics and has been in business for over 40 years. They have a parts floor and a audio video floor.


They stock NTE resistors in a large range of values

Look it is a great store ; https://www.youdoitelectronics.com

[Latole]

I found the hum. The positive signal wire fell off the square pre-amp plug.


A video I watched said that they are tricky and sometimes some tech's remake them.

You do a great job on this amp , congrat !

[pbman1953]

I found the hum. The positive signal wire fell off the square pre-amp plug.


A video I watched said that they are tricky and sometimes some tech's remake them.

You do a great job on this amp , congrat !

Thanks, but I have to give much of the credit this forum.

[pbman1953]

Tube question-


The v1 for this amp is a 12wd7.  After playing his a bit , and since the volume escalates very quickly, what lower gain tube can I use?






Thanks

[PRR]

> 12wd7

12DW7?? Altho I don't see one in the schematics in this thread.

>   ....the volume escalates very quickly

Are you trying it in the garage? Don't! The SVT is scaled for a coliseum.

Because the volume pot is LINear it will get real loud by "4" on the dial, and be real twitchy, in a small space. When your 40,000 screaming fans arrive, you will want that leverage.

[pbman1953]

> 12wd7

12DW7?? Altho I don't see one in the schematics in this thread.

>   ....the volume escalates very quickly

Are you trying it in the garage? Don't! The SVT is scaled for a coliseum.

Because the volume pot is LINear it will get real loud by "4" on the dial, and be real twitchy, in a small space. When your 40,000 screaming fans arrive, you will want that leverage.

There should be schematic on the first page of this post. It's being used in a studio. I'm just wondering if I could get a longer swing of volume. If it's no, I'll live with it

[sluckey]

The v1 for this amp is a 12wd7.

Never heard of that. Schematic shows 12AX7.

[pbman1953]

Here you go. This is my pre-amp but not my power amp. There were versions with all 12ax7's, this one is with 12dw7's


The back plate on my amp shows V9-SVT

[pbman1953]

Schematic posted in #131

[TenderTendon]

That schematic is interesting. Not very common to see a 12DW7 in a guitar amplifier, but 4 of them? Am I interpreting this schematic correctly, that there is high voltage passing through the speaker plug connector?

[pbman1953]

Hi All,


The correct schematic is 3 posts back


Thanks

[sluckey]

That schematic is interesting. Not very common to see a 12DW7 in a guitar amplifier, but 4 of them? Am I interpreting this schematic correctly, that there is high voltage passing through the speaker plug connector?

Take a look at some Magnatone schematics to see more 12DW7s. Good idea on the speaker plug.

[pbman1953]

Picture from inside the case

[acheld]

In the pre-amp there's a 40uf@450V

If you mean C12b, then you could place an 80uF cap there w/o problems, as long as it fits.   

[pbman1953]

In the pre-amp there's a 40uf@450V

If you mean C12b, then you could place an 80uF cap there w/o problems, as long as it fits.

I've already installed a 40/450. Is there an advantage with going with the 80? Plus it would fit

[acheld]

I've already installed a 40/450. Is there an advantage with going with the 80?

Without going to the effort to do a real analysis, I seriously doubt there would be a noticeable (or any) advantage to a larger capacitor in that position.