Vampower Mk1 Guitar Amp
- Thread starter CJ
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I have a couple of amps which are essentially the same thing, one is unbranded but probably had a Jennings logo when it was made, the other has a Triumph logo. The chassis and at least most if not all of the circuitry is the same as the Vampower branded amps.
I think they are really good for guitar and bass. One of these is my studio bass amp, it gets a lot more use than my B-15.
I think they are really good for guitar and bass. One of these is my studio bass amp, it gets a lot more use than my B-15.
Cool on the simulator!
was always wondering about doing a C core output transformer like Partridge used to build, now having second thoughts>
" One thing that did occur when changing from the Triumph based versions to the first Vampower amps was that of the Transformers. After first using Partridges, a certain person at Vamp decided the C core would transform the amp into a ‘wonder beast’. It did but- in the form of 'I wonder why I blew this amp up'. It took a lot of establishing. Bloody C & W guys again. Full power, full bass, full top, no mids, and thump the F##k out of it. (Give me a 'G' with the hinges off, tiger!) Valve bass flashover-the blight of many a valve amp. Turned out the output transformer was well coupled at low frequencies, (great for bass), that when coupled with top end, lightening level K volts were easily produced. Answer-de solder the straps and put cardboard strips between the cores to reduce the low frequency (below 30 Hz) coupling. This was no better than the original laminated type."
tone stack>
"JJ : Dave, why did you choose that unique eq tonestack for the vampowers?
DR : The sound thing like the Twin T middle? I was always playing around with getting sounds I wanted, and always frustrated with never getting them. At the time, this was the best way I could find. 'Ignore what was considered correct and do what pleases the head.' Middle was considered round the 1 k mark for music lovers everywhere. Not for me, and not for the guitar! I put it where I thought it sounded right. Same for bass as well., "
Double C core output>
was always wondering about doing a C core output transformer like Partridge used to build, now having second thoughts>
" One thing that did occur when changing from the Triumph based versions to the first Vampower amps was that of the Transformers. After first using Partridges, a certain person at Vamp decided the C core would transform the amp into a ‘wonder beast’. It did but- in the form of 'I wonder why I blew this amp up'. It took a lot of establishing. Bloody C & W guys again. Full power, full bass, full top, no mids, and thump the F##k out of it. (Give me a 'G' with the hinges off, tiger!) Valve bass flashover-the blight of many a valve amp. Turned out the output transformer was well coupled at low frequencies, (great for bass), that when coupled with top end, lightening level K volts were easily produced. Answer-de solder the straps and put cardboard strips between the cores to reduce the low frequency (below 30 Hz) coupling. This was no better than the original laminated type."
tone stack>
"JJ : Dave, why did you choose that unique eq tonestack for the vampowers?
DR : The sound thing like the Twin T middle? I was always playing around with getting sounds I wanted, and always frustrated with never getting them. At the time, this was the best way I could find. 'Ignore what was considered correct and do what pleases the head.' Middle was considered round the 1 k mark for music lovers everywhere. Not for me, and not for the guitar! I put it where I thought it sounded right. Same for bass as well., "
Double C core output>
Attachments
Vampower Mk 3 bass amp circuit>
(wow, when did we get pdf uploading installed? cool!)
(wow, when did we get pdf uploading installed? cool!)
CJ said:Vampower Mk 3 bass amp circuit>
(wow, when did we get pdf uploading installed? cool!)
Weird that there is no connection shown between the cathodes and the suppressor grid on the EL34's or is that jut ASSumed to be the case ?
It's implicit since the EL34's are drawn as tetrodes.Rob Flinn said:
I would think the 22k bias pots should really be 220k.CJ said:
Individual Bias on output tubes with a 1Ω cathode resistor for easy read out on a meter. In 1969. Very smart. Might have been in the Brimar amp books or something. Like it.
I’ll want to try the eq to hear what it sounds like. The phase drive looks different on power amp.
I’ll want to try the eq to hear what it sounds like. The phase drive looks different on power amp.
It's one of the few possible topologies; one side is a basic common-cath stage and the other is a unity-gain inverter under almost 100% NFB. As a result their are significantly mismatched in terms of the impedance they present to the grids of the output tubes. The drive voltages are perfectly matched, though, as long as the input and NFB resistors are equal. The voltage balance is kept close to perfection whatever the tube characteristic's drift.fazer said:
> I would think the 22k bias pots should really be 220k.
I vote for 22k.
Four of those with the 10k under allows a good spread of bias (at least for days when tubes were consistent).
220k four times with 10K allows way too much bias change. Also way too much resistance in the grid return. (We are already far past the datasheet's limit.)
If the pots are worn, with today's tubes, I might go up to 50k to get a little more range.
I vote for 22k.
Four of those with the 10k under allows a good spread of bias (at least for days when tubes were consistent).
220k four times with 10K allows way too much bias change. Also way too much resistance in the grid return. (We are already far past the datasheet's limit.)
If the pots are worn, with today's tubes, I might go up to 50k to get a little more range.
I'm referring to this schematic.PRR said:
http://www.chambonino.com/work/vampower/vampwire2b.jpg
The series resistor is 47k. With four 22k pots, the max bias voltage is about -15V.
Now, if the pots are actually 220k, the series resistor cannot be 47k.
In fact this schemo is very dodgy, since the absence of a resistor to ground allows setting 0V bias, which is a receipe for disater.
Indeed, the Bassmaster bias topology is very different, and the 1.8k series resistor in the CRC filter is perfectly compatible with 22k pots.
> I'm referring to this schematic.
Ah, OK.
Yes, the to-zero bias is reckless; we hope the as-built amps had a stopper.
As for the supply-- these clamp-diodes are subtle, and this one is worse than most. I discovered I had to sim both the bridge and a bridge-load, or the bias would not develop.
For 5.5k (four 22k) I get -26V bias; for 55k I get a long slope toward -140V.
140V is excessive.
26V is marginal BUT if we assume a 10k stopper we get -60V to -39V which is not wrong; 6.8k stopper may be the ticket.
I *really* prefer a cheap 50VAC winding, rather than long strings of parts with high peak stress and no 2-thumb way to guestimate happy operation.
Ah, OK.
Yes, the to-zero bias is reckless; we hope the as-built amps had a stopper.
As for the supply-- these clamp-diodes are subtle, and this one is worse than most. I discovered I had to sim both the bridge and a bridge-load, or the bias would not develop.
For 5.5k (four 22k) I get -26V bias; for 55k I get a long slope toward -140V.
140V is excessive.
26V is marginal BUT if we assume a 10k stopper we get -60V to -39V which is not wrong; 6.8k stopper may be the ticket.
I *really* prefer a cheap 50VAC winding, rather than long strings of parts with high peak stress and no 2-thumb way to guestimate happy operation.
Attachments
Yes, figured out the same.PRR said:
Yes, I believe the schemo is not 100% proof.
Indeed. I'm currently fighting with a rewound PT for an Ampeg VT22. Adjusting bias is a PITN. I think I'll have an other rewound with a separate bias winding.
PRR said:
Yeah, I think the relationship is understated on that page. The Vampower amps just are not that different than the Johnson/Jennings/Sola Sound/Triumph branded heads made by Triumph, the chassis are definitely the same, and the circuitboards are very similar.
I still love the B15 and would pick it for some things. Part of it is the speaker pairing. The Triumph into a Bergantino 310 puts out some great chewy mids and speaks with bigger cabinet authority in the lows even without that much volume. The B15 is healthy and vintage correct but sounds bandwidth limited in comparison. The B15 has an Altec like Jamerson's , I think I used to like it a little better with the original CTS, even though that is even more bandwidth limited.
> Ampeg VT22. Adjusting bias is a
I'm not telling you what to do. Especially on a VT22 which, IMHO, is worthy of respectful restoration.
As a general thought for lurkers: if you are tired of fighting dog-leg bias supplies:
Get a 120V:12V transformer. As small as you can trust. (230V folks can find 115V+115V windings.)
Wire the "12V" side to your 6VAC heater lines. Secondary is now about 60VAC, which will simply rectify-out to over 80V of DC. Do some resistor calcs to hit your target.
And-- unknown target: Figure/find your Vg2, and your Mu(g2). Say Vg2 is 400V and Mu(g2) of 6L6 6V6 EL34 is 10 (EL84 is 18). 400V/10 is 40V. A hot near-A bias is 0.6 of this, 24V. You do not want the tech to accidentally dial-down any further (hotter). A cold bias is 1.2 of this, 48V. You may want this extreme for initial smoke-test, or for very over-Volted designs.
I'm not telling you what to do. Especially on a VT22 which, IMHO, is worthy of respectful restoration.
As a general thought for lurkers: if you are tired of fighting dog-leg bias supplies:
Get a 120V:12V transformer. As small as you can trust. (230V folks can find 115V+115V windings.)
Wire the "12V" side to your 6VAC heater lines. Secondary is now about 60VAC, which will simply rectify-out to over 80V of DC. Do some resistor calcs to hit your target.
And-- unknown target: Figure/find your Vg2, and your Mu(g2). Say Vg2 is 400V and Mu(g2) of 6L6 6V6 EL34 is 10 (EL84 is 18). 400V/10 is 40V. A hot near-A bias is 0.6 of this, 24V. You do not want the tech to accidentally dial-down any further (hotter). A cold bias is 1.2 of this, 48V. You may want this extreme for initial smoke-test, or for very over-Volted designs.
user 137017
Well-known member
I have just seen one of these on fleabay. Listed as parts only spares or repair. The workmanship was evidentlt 1st class when new now thete are a few burnt resistors, a crack or two in the boards. Listed at £1500 this could be a real investment or just a money pit 40-50 years old it will need a total rebuild. To be honest i would like it but not at that price
