Bassman build voltages...

[Icetech]

Just curious if anyone that has done a bassman build could lemme know around what b+ voltages they got? i cant seem to get over 385 with tubes in..

Just mesuring off the rectifier with no tubes in i only get 398v i see on hybrid-a it should be more in the mid to high 400's... any ideas?

P.S. this transformer is model 022814

[Bennypapa]

THat math adds up. 330 vac should only net you around 380~390vdc when loaded by the circuit.

Just use it as is and see how you like the sound.

How does it sound or have you built anything past the power supply yet??

Bennypapa

[Icetech]

sorry.. problem is i am getting 398v without it loaded... i have the wire from the rect to the rest of the amp totally off and getting 398...

I checked both taps from the PT and get 330-334 on each..

so that should be 330x1.4=462...

gotta be something with the rect. circuit, on the bassman it isn't the normal 4 diode sqare shaped one.. its more like

--- --- \____output
--- --- /
6 diodes.. wonder if i should switch it to a normal setup..

[Icetech]

Well... im stumped.. replaced the diodes.. triple checked it all.. cant get over 404v without a load.. the PT is 330-0-330

Sorry bout this post.. first time using SS rect.. usually plug a tube in and let er rip:)

[Bennypapa]

HMMMM
I must have been looney when I posted that last reply.

according to PSUDII

http://www.duncanamps.com/psud2/index.html

I get right at 450vdc simulated at the first filter cap in the following setup

1n4004 fullwave rectifier into 100uf, 90 ohm choke, 100uf

HMMMM

Are the filter capacitors hooked up. Maybe you missed a connection there?
some multimeters give an average dc of an AC voltage. Without the caps there would be one sided ac on there and maybe that would be averaged by your meter to 398???


Sorry about the bad math earlier. I don't have any idea where I got that.

Anyway, download that PSUDII software, I use it all the time. Made by some folks that are a whole lot smarter than me!

Bennypapa

[Normster]

That sounds about right. I'm getting 438VDC at the plates with the power tubes removed. From the rectifier, I'm getting 443VDC. (500 Ohm resistor for choke.) Tubes in with the amp at idle, I have 424VDC on the plates. Getting 332VAC on each leg of the PT with 118VAC house current.

[Icetech]

Thanks for posting all that....

I get 334AC at the PT outputs... run through the rectifier and comes out 404DC thats with nothing hooked up.. with the amp loaded and power tubes in i am only getting like 350V at the power tubes..

Thinking i just have a weak PT or something.. I was actually playing a bit tonight and it doesn't sound bad.. one thing i was curious about is, could i get away with running 6v6's at the lower voltage anyway? which would make it quitier and me happier..

[mlp-mx6]

6V6s will take that voltage easily. The difference will be that you will need to adjust the output impedance down (or use a higher speaker) to compensate. 6V6s want approximately 2x the impedance of 6L6s. (6600 instead of 3400) You can "trick" it by using your 8 ohm speaker on the 4 ohm tap, etc.

Of course, you may prefer the tone with the "mismatch" - there's no harm in it. Some amps don't even list the impedance values - just consider them as slightly different tones.

Oh, and you'll need to adjust the bias - and perhaps even the bias supply - for 6V6s.

[Icetech]

Ok... this is making me nuts.. just cant let it go... so here goes...

in the image below i am using the rectifier setup on the bottom Left "full wave diode rect."



Using this with nothing hooked up to the rect but my meter=404VDC..

I tried using a bridge rect. (top right) and got 812VDC..

my wall voltage (measured at the power switch inside the amp) is 122V

Output from the PT is 344VAC on each leg... total output from rect is 404..

from the schems for hybrid-a i have seen the rect is setup right.. would anyone else have a idea for the low voltage?

And sorry to keep harping on this but its just really buggin me...

P.S. the bias circuit seems fine giving me exactly -30 to -60 V, just mentioning in case that matters...

[mlp-mx6]

Is your center tap grounded well? (Red/Yellow in your picture) Is there ANY chance that that ground connection is not solid?

[Icetech]

No... restripped and soldered...

[mlp-mx6]

General check of all power supply grounds? Especially the main filter cap grounds - plate and screen.

Geez, this is a weird one.

[Icetech]

well.. thing is.. this is without any filter caps grids or anything even hooked up....just the PT and rect...

on the up side i just redid the tone stack and its sounding pretty good:)

way too much gain on the clean channel though:( thinking the low voltage might not be helping that

[llemtt]

Icetech is your AC meter a "true rms" meter?

It seems that your 344 VAC is not "rms"!! It sounds more like 285 VAC rms which explains why you end up with only 404 VDC after (solid state) rectifier.

Teo

[llemtt]

Sorry Icetech I missed the fact that your PT is a 22814 which is supposed to output 330 VAC rms!

You have to use 1N4007 diodes (mandatory), 1N4004 cannot withstand the back voltage!!

Teo