Ampeg V4 not very loud.

[jvm]

I have a Ampeg V4, master volume version. Came in with two can caps hanging loose so I did not power it up. Replaced all electrolytics, cleaned pots and jacks, re soldered all tube sockets. Set bias at 38mA per tube. Amp works now and all functions work perfectly. The only problem is that it seems low on volume. Seems like 20 watts rather than 100watts. I have another V4 on hand that is the non master volume model and it just eats this one alive as far as volume. I have checked all voltages against the schematic and they all seem acceptable to me. ( They are generally high of course) Has anyone run into this with one of these amps before? The second V4 is having arcing and other issues and I have not dug into it yet. I'm hesitant to use for comparison testing.

http://www.ampegv4.com/images/schema...VT-22_1977.jpg

[jvm]

Forgot to mention that I have subbed known good tubes in every position. I also just ran the other V4 preamp into the power amp input on the weak V4 and it was STUPID LOUD! So I have narrowed it down to the pre amp.

[Leo_Gnardo]

Forgot to mention that I have subbed known good tubes in every position. I also just ran the other V4 preamp into the power amp input on the weak V4 and it was STUPID LOUD! So I have narrowed it down to the pre amp.

Thank goodness for that: your output transformer must be OK. Not something you'd want to pay to replace. How's the supply voltages to the preamp? Sometimes resistors go open-circuit or nearly so. On occasion I've found open plate or cathode R's in Ampegs of this vintage. Also resistors that have bad solder connexions. Some of those old interstage caps get funky too, especially the multicolor "tropical fish" style. If the outside layer is cracked & crumbling, change it out.

Stupid loud. Yes, that's what they do. DEAFinitely a rock amp.

[jvm]

Problem solved! I signal traced the preamp up to C203 and C204 at the midrange pot. I had very little signal at C204. I found R208 (56K) measuring 71k and R211(47k) open. Replaced both and the amp is back to it's former glory! Loud and proud!

[g1]

One more thing I always check on these is the solder on the board mounted sockets for the preamp tubes. At the age of these amps, the heat cycling has often loosened up those solder joints.

[Leo_Gnardo]

I found R208 (56K) measuring 71k and R211(47k) open. Replaced both and the amp is back to it's former glory! Loud and proud!

Yeaaahhh buddy - good find! I don't know why but 47K commonly fail in those V-era Ampegs. A decade later, similar problem in Hafler solid state power amps.