New old amp day - Dynacord Eminent II

[Beer of the Bass]

I've always enjoyed having interesting old valve amps around, but I've been without one recently. I had a smaller Dynacord Bass King T for a little while, so when I spotted this Dynacord Eminent II on eBay, I decided to go for it. It's an unusual design; intended as a PA mixer amp, it has transistor preamps with a valve phase inverter and power stage. Even more unusually, it runs a high plate voltage of around 750 volts in order to achieve an output of 80 watts from a pair of EL34 valves, which would typically be used at around 400 volts in a 50 watt amp. They were made in Germany from the late 60s to the end of the 70s - this one is dated May 1978. It has the benefit of being very compact for a valve amp of this output and having a perspex front panel which is illuminated in green when switched on - I'm a sucker for that sort of kitsch!
I was fairly lucky considering that I bought it unseen. It arrived in working condition; there are no issues with hum or noise, it has the correct fuses and the valves are not red-plating or microphonic. The valves are a Telefunken ECC81 and a pair of Hoges EL34, which I gather are re-badged RFT EL34s. I haven't had the chance to check voltages or bias yet, but I will do that.
While the amp doesn't seem to require troubleshooting, I still intend to replace the filter capacitors for the HT and bias supplies and replace the bias trimmers with more modern types just to make it a little more reliable. One section of the can capacitors has been disconnected and replaced with a pair of lower voltage rated capacitors in series, though from the appearance of the capacitors this must have been done more than 20 years ago, as the replacements were made in West Germany.
I have only had a quick play through it so far, but it sounds good - very clean and clear. The input impedance is low by modern standards so it can sound dull when plugging a passive bass straight in, but a simple buffer such as a Boss tuner on bypass sorts that out.
I might add a direct input to the power amp section so that I can build a B15n style preamp in a small box to use with it - this feels less invasive than replacing the preamp section of the Dynacord (which I've heard of other people doing).
The cab in the photo is a small DIY 1x10" which I use for quieter settings, though the Dynacord will mostly be used with the pair of 1x12" cabs I am building at the moment.

Edited January 20, 2016 by Beer of the Bass

[VTypeV4]

Super cool..

I read on John Chambers' site about raising screen and plate voltages to run 200w from 4 x EL34. Very interesting stuff.

[Twincam]

Very very cool. Any pics of its internals?

[Beer of the Bass]

[quote name='Twincam' timestamp='1453394620' post='2959129']
Very very cool. Any pics of its internals?
[/quote]

I haven't taken any internal pictures of mine, but there are some of the same model here: [url="http://www.radiomuseum.org/r/dynacord_eminent_ii_2_t.html"]http://www.radiomuseum.org/r/dynacord_eminent_ii_2_t.html[/url]
It's quite a tight layout in there - servicing it will be interesting...

[Merton]

I love the look of this, it's cracking

[JapanAxe]

750V? Wow!

[Beer of the Bass]

After leaving it sitting for a few weeks, I've got round to doing some work on this. Since the original style screw-mount filter caps are hard to get and pricey, I've made up an eyelet board to take modern axial caps. I've also replaced the bias capacitors and trimmers on the power amp board (as apparently the trimmers failing is a common fault on these) and a couple of drifted resistors. While it was working OK with the original parts and I might have got away without touching it, I want to make it as dependable as possible.



I've put it all back together, though I still need to check it over, set the bias and check voltages before I give it a try.
Next I need to decide whether I will leave the preamp side of the amp as stock or modify it. At the moment it's essentially a solid-state mixer amp in front of a valve power stage, so isn't as much fun as it could be as a bass amp. I'd like to make a dedicated bass preamp for it, but I could either take out two of the input channels and build it inside the box, or I could make a standalone preamp and add a power-amp input to the back of the Dynacord. Having it all in one box would be convenient and less work, but a standalone preamp could be a bit more versatile...

[Twincam]

So how does it sound with a bass?

[Beer of the Bass]

[quote name='Twincam' timestamp='1462894051' post='3046746']
So how does it sound with a bass?
[/quote]

It's very clean and quite neutral sounding, though the bass and treble controls aren't very useful for bass as they're centred fairly high. But since I have this nice valve power stage in a compact package, the temptation to put a classic valve preamp in front of it is hard to resist.

[Twincam]

Well if you do I would like to hear about it and pics are good.

[fuzzonaut]

Nice!

I have one of those, in a wooden enclosure. It was my first amp with tubes in it.
When I had it serviced a few years ago, I got a power amp input installed (at the back).
I'd go with this solution, as it also leaves you with the possiblity to use the full amp as well.

After using it as a bass amp, I now use it as a "mixer" amp to run (and mix) different stuff (synths, vocals, drone boxes) through the channels.

[Beer of the Bass]

[quote name='fuzzonaut' timestamp='1462976249' post='3047471']
Nice!

I have one of those, in a wooden enclosure. It was my first amp with tubes in it.
When I had it serviced a few years ago, I got a power amp input installed (at the back).
I'd go with this solution, as it also leaves you with the possiblity to use the full amp as well.

After using it as a bass amp, I now use it as a "mixer" amp to run (and mix) different stuff (synths, vocals, drone boxes) through the channels.
[/quote]

I was thinking about only removing the two input channels on the right, fitting a simple (B15n based) valve preamp in their place and sending it's output straight into the power amp. The two channels on the left would still be there, and the three central controls would still work on those. So it would still keep most of the original functionality of the amp, just with fewer input channels. It could also be put back to the original state quite easily, if it doesn't work out.
The more I think about it, I reckon this is the route I'll try.

[fuzzonaut]

[quote name='Beer of the Bass' timestamp='1462985299' post='3047604']
I was thinking about only removing the two input channels on the right, fitting a simple (B15n based) valve preamp in their place and sending it's output straight into the power amp. The two channels on the left would still be there, and the three central controls would still work on those. So it would still keep most of the original functionality of the amp, just with fewer input channels. It could also be put back to the original state quite easily, if it doesn't work out.
The more I think about it, I reckon this is the route I'll try.
[/quote]

Ah, I see.
Sounds like the perfect plan!

[Beer of the Bass]

I've now got it reassembled and fully working with the new filter caps and a fresh pair of JJ E34L valves. Here's a gut shot before the valves went in - it's tightly packed in there!


After checking the voltages and setting the bias, I had a play with one of my DIY 1x12 cabs. It's a nice sounding little rig, though I haven't had a chance to turn it up yet. I'm pleased at how quiet it is in terms of hiss and hum - I've had modern micro heads with more hiss than this!
I definitely need a more bass guitar voiced preamp though, as I like to boost the highs a bit to bring some articulation out of my flatwound strings. The treble controls on this work so high up that I can barely hear a difference when playing with a tweeterless cab.
It looks good with these cabs too - I think it will be fun trying it with the pair of them next time I jam...

Edited May 15, 2016 by Beer of the Bass

[Pentode]

That's lovely! Also you've done some nice, tidy work on it

[Twincam]

[quote name='Beer of the Bass' timestamp='1463328985' post='3050512']
I've now got it reassembled and fully working with the new filter caps and a fresh pair of JJ E34L valves. Here's a gut shot before the valves went in - it's tightly packed in there!


After checking the voltages and setting the bias, I had a play with one of my DIY 1x12 cabs. It's a nice sounding little rig, though I haven't had a chance to turn it up yet. I'm pleased at how quiet it is in terms of hiss and hum - I've had modern micro heads with more hiss than this!
I definitely need a more bass guitar voiced preamp though, as I like to boost the highs a bit to bring some articulation out of my flatwound strings. The treble controls on this work so high up that I can barely hear a difference when playing with a tweeterless cab.
It looks good with these cabs too - I think it will be fun trying it with the pair of them next time I jam...


[/quote]

Cool looking rig. Be interesting when you do something about the pre.
I know what you mean about the treble for articulation, I too use flats and often depending on the amp have to put a little more treble on.

[Beer of the Bass]

Wow, has it been a year and a bit since I got this? I'm terrible at staying focussed on a project!

I've just finished modifying the Dynacord with a valve preamp, replacing two channels of the original transistor preamp. I've squeezed a little board in with a single 6sl7 valve and built a James style tone stack on the back of the pots, it's essentially a late-60s Ampeg B15n preamp circuit. I found that the new preamp didn't quite have enough output to drive the Dynacord power amp to its full output, so I've cheated a little and used a simple high-voltage FET stage in between the tone controls and power amp board. The new preamp section is on the top right in this picture. It's mounted using right angle brackets to holes that were already in the chassis and I've kept the parts that were removed, so it could be done without hacking the amp up too much. The rest of the original transistor preamp is still in place, just with two identical channels instead of four.


I won't have a chance to try it out at band volume until Saturday, but it's sounding good in the house. The new preamp is very good at doing that kind of subtle grit that barely sounds dirty but thickens the sound right up, and the power amp is made to run on the clean side of things. We've been recording our rehearsals lately, so I might be able to come up with an audio clip of it doing its thing. If it gets through that first rehearsal without going bang, I'll try gigging it...

[discreet]

Wow, that's the ocelot's knockers!!

[Beer of the Bass]

I'm just back from jamming with it, and I'm well chuffed with how it sounds. It's an easy sound to fit into the mix; plenty of mids without sounding boxy and a nice bit of grunt when pushing the front end. It held it's own with the drums and guitar using a single one of my 1x12"s, so it should be good for most of our gigs with the pair of them. I might fit a bright switch in the empy jack hole though, as a touch more edge wouldn't go amiss on a couple of songs. So I think this will be coming out on some gigs with the bluesy rock trio I'm playing with.
Now I need to figure out a strategy for using it on PA-assisted gigs. I'd like to get some of the amp-y colouration into the FOH, but I need to consider the soundguy acceptance factor. Possibilities are;
1- Add a preamp line out to the back of the amp, before the master volume. This could go through my DI box (a BSS AR116) into the PA. The DI has a switchable lowpass which would serve as a simple speaker emulation. This would only capture the preamp colouration, but I think that's a lot of what I'm hearing. It also has the advantage of being unaffected by the master volume setting.
2- Use the DI box with 40dB pad engaged, running off the speaker output. This would get more of the amp sound but the level would vary depending on the amp volume.
3- Obtain and carry a suitable mic. I've heard good things about the AKG P2.

I suspect the first option is the least likely to annoy venue sound guys, but the other two might also have their plus points.

[DIYjapan]

Hello, question not about the amp but the cabinet in that first picture. What is it? DIY? Looks really sweet.

[Beer of the Bass]

It's a little DIY 1x10", made from birch ply and stained. I have a Faital 10FE200 in there which is a cheap driver with modest excursion, but has nice even mid response and decent treble for a single driver cab. I use it for double bass mostly, and my 1x12" cabs do the electric bass gigs.

[Dan Dare]

Nice. Dynacord is very high quality kit. I had one of their valve amps briefly a while back, but the output trannie failed (it was an old amp and I bought it used, so no criticism of Dynacord intended) and the cost of replacement was prohibitive. Very fine sound whilst it was working.

[catalin gramada]

Hi. You Dynacord is sort of HiFi amp.In consequence they used lot of negative feedback to improve the liniarity (18-20db as it looks-I think) I bet you can cut to 10-12 db arround and still can have good bass not boomy reponse. So, replace the feedback network with some more convenable in 1:10 to 1:15 ratio should be enough.( Keep in mind some bias voltage is developed over series feedback resistor and secondary winding so better to replace with sort of 2k2 bypassed with 100uF in first half ecc81 cathode and add 100ohm to ground. Use 1k-1.5k from junction between 2k2 and 100ohm and run to 8-16 ohm secondary tap. Now you should have enough room from you 6sl7 b15 type preamp 4Vpk arround think to push you Dynacord power stage to the proper drive. You can squeeze a litle bit more excursion if you change 220k from cathodyne grid to 470k.
Sorry for my broken english, hope it have sense.
Cheers

Edited October 23, 2017 by catalin gramada