Webster 166-1 volume issue

[Resonator Guy]

Gentlemen, (and ladies, if any) I have two problems. First I cannot post pictures to this site since I got my new laptop running Windows 8. So I will have to try and explain as best I can.
I recently got a Webster 166-1 amp. This used to have two inputs, one for a phono and one for a mic (karaoke?). It has had a 1/4" jack installed for guitar running through the phono volume. Someone has recapped it and there is absolutely no hum. It just doesn't play very loud. I don't play real loud, but I want it to work correctly. My silverface Champ or Garnet Celebrity will blow it out of the room and they only have one 6V6 apiece.
It has a 6AT6 preamp (replaced by a 6AV6), 12AX7 PI, two 6V6s and a 5Y3. A schematic is available here Webster Chicago and interior shots here Webster Chicago PA Amp Model 166-1 - a set on Flickr . I actually can cut and paste here. I may try that with pics later.
All I have done is remove the two inputs wiring, which made no difference to the volume. I do wonder about a RIAA curve or some such as I know hooking up anything to a phono input on a HiFi receiver doesn't work well.
The amp sounds real good, great tone, but just not nearly enough volume for 2 6V6s.
Any suggestions as to what to start checking? I do want this beauty to play well.
Thanks

[Jazz P Bass]

Do the voltages on the amp match the schematic?
I would place a meter. set to read volts ac, and measure the output voltage at the speaker connections,with the amp cranked.
That voltage , squared & divided by the speaker resistace is the output power.
With 280 plate volts you are probably looking at something like 10 watts.

[Resonator Guy]

Do the voltages on the amp match the schematic?
I would place a meter. set to read volts ac, and measure the output voltage at the speaker connections,with the amp cranked.
That voltage , squared & divided by the speaker resistace is the output power.
With 280 plate volts you are probably looking at something like 10 watts.

Jazz, with my very inexpensive Radio Shack meter set at 200 VAC I get a reading of 1.4 on one tube and 2.3 on the other. Seems a little low even if that is actually 140 and 230. Also slightly unbalanced.

[Jazz P Bass]

What I was asking is #1: are the Vdc readings in line with the schematic.
Like B+, preamp plate & cathode voltages.
#2: get a Vac reading of The Speaker leads at full blast.
You want to know what the power level of the amp is.
Then you can compare it to other amps.

[52 Bill]

Jazz, with my very inexpensive Radio Shack meter set at 200 VAC I get a reading of 1.4 on one tube and 2.3 on the other. Seems a little low even if that is actually 140 and 230. Also slightly unbalanced.

How did you get these readings? The output is wired very differently than most amps, the two output tube cathodes are connected directly to the output transformer secondary winding and are grounded through the center tap of the secondary.

If you are going to try and get a wattage reading you will need to read directly across the speaker terminals or a load resistor.

[Resonator Guy]

Gotcha.
The reason I was reading Vac at the plates is because the speaker leads run from them to the speaker and I figured the readings would be the same at either end of the wire.

[Resonator Guy]

I am going to try to get the other voltage readings now. I say try because, next to trying to draw schematics, I like this the least.
Across the speaker terminals ( one probe on one terminal and the other probe on the other terminal ) with my meter on the 200 Vac setting, I read .2 Vac. I don't really care what wattage it roughly produces; I just don't think it is working optimally.

[Resonator Guy]

Well I reviewed the schematic and took voltage readings everywhere I saw a voltage noted on it. Mine are almost all a little off. Here goes.

6AV6 - pin 7 - 61 - schem says 45

12AX7 - pin 1 - 98.6 - schem says 105
pin 6 - 83 - schem says 105
pin 3 & 8 - 1.1 - schem says 1.2

6V6 - pin 3 - 284 - schem says 280
pin 4 - 282 - schem says 275
pin 8 - 20.5 - schme says 15

6V6 - pin 3 - 283 - schem says 280
pin 4 - 281 - schem says 275
pin 8 - 20.4 - schem says 15

Those were all I read. How do they look?

[Jazz P Bass]

I just don't think it is working optimally.

But that little piece of information is required.
I do not own a cheap meter so I don't know what that .2Vac means.
Also, what is the speaker DCR?

[Resonator Guy]

But that little piece of information is required.
I do not own a cheap meter so I don't know what that .2Vac means.
Also, what is the speaker DCR?

?????
The speaker DCR is 5.8 ohms.
As for the .2 Vac that is the result of the measurement you suggested earlier to determine the wattage. Measure Vac across the speaker terminals with the amp cranked??
That is the best I can do. I still don't understand why but that is it. I am slowly but slowly learning this stuff but short forms, assumed knowledge and stuff like that don't help.

[Jazz P Bass]

Sorry I was not more helpfull.
It is simply that I do not understand the .2Vac reading.
.2 x .2 / 5.8 is nothing.

[sgelectric]

Resonator Guy, A few observations:

You stated in your OP that you are using the phono volume control in your amp with the 1/4" guitar input.Be advised that the phono input bypasses the 6AT6(6AV6) and goes straight to the 12AX7.
These amps were not made to run with Magnetic phono cartridges but rather with high output Crystal cartridges.The RIAA curve does not apply in this case.

You will have more gain by using the Mic input and its associated circuitry.

If you really want to make it suitable for guitar, you should also consider changing the grid leak/contact bias input to a more conventional cathode(self) bias input stage.

Hope some of this is useful.
SG

[Resonator Guy]

Thanks SG. |I just tried tying into the mic input and got nothing different. Any suggestions on how to do that. The mic and phono both lead to the same tab on the phono volume control. It is that way on both sets of pics I have found on the web. I move the jack's leads to the back of the mic input but it didn't do anything at all . the phono volume continues to control the thing.

[madkatb]

Did the recap include C2 and C3, the cathode bypass caps? If they are old and leaky they could be the problem, especially C3 as the power tube cathode voltages seem high.

[Resonator Guy]

Those bypass caps have been changed. They were replaced by 15mf and look pretty recent.