Dynacord Imperator valve amp.

[Maude]

I was having a quick clear out of a large trunk in our living room and found an old Dynacord valve amp that someone gave me years ago. I'd taken it apart 15 to 20 years ago as, from memory, it was a bit crackly. I never thought much of it so the front and rear panels, knobs and all the screws had got slung out when the drawer they were stashed in got replaced, too be followed by the amp at some stage. Anyway roll forward many years and I discovered it and thought I'd see if anyone wanted it instead of going to the tip. Now I'm having thoughts on building a flip-top type combo (thanks to @rubis)  as I've got a couple of really nice Celestian 15s in storage that are in the way as well, so all it'll cost me is materials and time. 

Anyway enough rambling, the amp is, from pictures I've googled as the front and rear panels are long gone, is a Dynacord Imperator from the late 60s or early 70s, 50-80 watts depending on different opinions and apparently transistor pre and an ECC81 and two EL34's in the power section. I've turned it on in standby and it lights up and all three valves glow, it's really dirty/dusty in there so needs a good clean but what else should I look out for before I try plugging a bass and cabinet in to see if it's worth bothering with. I'm no electrician so talk to me like I'm an idiot. There's four 'outs' on the back, one marked 16ohm and three marked 8ohm, I assume just plug an 8ohm cab into any of the three marked 8ohm. 

Lastly as this must be boring now, has anyone used one as a bass amp and if so, was it any good? 

Pictures from Google search;

 

[Beer of the Bass]

I have an Eminent 2, which is the same power amp with a four channel preamp.  They're well built amps intended to run very clean.  I found the original preamp a bit uninspiring on mine, so took out two of the channels and built a valve preamp in there. 

The power ratings can be confusing as this era of Dynacord amps had models with 2x EL34 valves at two different power ratings.  The Bass King T and Eminent I were 40 watts, with the Imperator and Eminent 2 at 80 watts.  The 80 watt models used a dual-rail power supply which puts around 750V on the EL34 plates.  Because of the high voltages and unusual layout these might not be the ideal platform to learn on if you're not familiar with working on valve amps, so you may want to have it checked over. 

[rubis]

What a cool project Maude, I'll be watching with great interest 

[Maude]

2 hours ago, Beer of the Bass said:

  I found the original preamp a bit uninspiring on mine, so took out two of the channels and built a valve preamp in there. 

Thanks for the info @Beer of the Bass. 

I also have a Peavey Max pre amp cross over unit which I used to use years ago when running a stupidly large bi-amped rig (that's what the Celestians are from), the solid state pre never worked and then crossover started playing up but the valve pre was lovely sounding and works perfectly. 

I seem to have all the parts to make a really cool rig, just not sure what to do with it. 

 

[Maude]

I took the valves out to give them a clean as they were thick with dust and all markings promptly wiped of as well. They were Telefunken so I assume original. One looks perfect but one has blackened on the inside creating a mirrored look from outside. Is that normal for old valves or is it on the way out? They both glow the same when powered up. 

You can see the 'mirroring' on the left one around both sides of the flat plate, I guess this is the hottest area on the outside where the plate is closest to the glass. 

[Maude]

The markings on the smaller one before I wiped them off. 

[Beer of the Bass]

On 06/10/2019 at 10:43, Maude said:

I took the valves out to give them a clean as they were thick with dust and all markings promptly wiped of as well. They were Telefunken so I assume original. One looks perfect but one has blackened on the inside creating a mirrored look from outside. Is that normal for old valves or is it on the way out? They both glow the same when powered up. 

You can see the 'mirroring' on the left one around both sides of the flat plate, I guess this is the hottest area on the outside where the plate is closest to the glass. 

Hard to say from a photo alone, but it's likely that one valve may have been running hotter than the other.  With an amp like this that's been out of use for years I'd really want to do more than visual checks before powering it up, like checking that the bias supply is present and correct on both EL34 sockets.  But it might be wise to find someone who's familiar with doing this safely.

[itu]

Many tubes are coded with several numbering systems, like

ECC81 = 12AT7 = B309 = 6060 = M8162

EL34 = 6CA7 = KT77 = 6P27S (the last one should be written in Russian letters)

First letter E tells, that the filament voltage is 6.3.

ECC81 = C is a small signal triode and CC tells, that it is a double. There are two triodes in that single tube; 8X-series has 9 pins in the base.

EL34 = L is a power tube; 3X-series has an octal base.

As @Beer of the Bass wrote, usually a pair of EL34s put out 55 W, but 80 W is a pretty special - and hot - configuration. Beware, each wire may have a specific reason in being where they are.

Tubes are interesting components. There are some ultra special applications (like broadcasting, EMI resistant components, nixie tubes, radar, X-ray, kW class output, water-cooled stuff etc.) that are or have been possible only with tubes.

The next video is not for those in a hurry (17 minutes). A French gentleman, Claude Paillard, makes tubes from scratch at home. Enjoy!

https://www.youtube.com/watch?v=EzyXMEpq4qw

Edited October 7, 2019 by itu

[Reggaebass]

What a great project, and there’s something about looking at valves that I find really fascinating 🤓

[Maude]

8 hours ago, Beer of the Bass said:

Hard to say from a photo alone, but it's likely that one valve may have been running hotter than the other.  With an amp like this that's been out of use for years I'd really want to do more than visual checks before powering it up, like checking that the bias supply is present and correct on both EL34 sockets.  But it might be wise to find someone who's familiar with doing this safely.

Thanks @Beer of the Bass, I thought logically it must be the bias out making one run hot. 

I'd like to learn about these things and although I know little about it now I grasp things like this pretty quickly. I'm not going to do anything silly though. I've had enough shocks to know I don't much like them. I found a retired audio engineer who liked to tinker a few years ago who looked at an amp for me, I might see if he's still tinkering. 

Ideally, and this may seem mad or just plain unfeasible, I like to take out the solid state pre and put my Peavey valve pre in, remove all the unnecessary inputs just leaving one and then build a shiney housing to show off the valves, like the Ashdown Little Bastard with the top removed. 

Edited October 7, 2019 by Maude

[Maude]

Thanks @itu, some good info there and I'll watch the clip later when I've got some peace and quiet.

@Reggaebass, I know what you mean. There's something 'mad scientist' about them that this glowing glass tube is amplifying my sound. 

[Beer of the Bass]

35 minutes ago, Maude said:

Thanks @Beer of the Bass, I thought logically it must be the bias out making one run hot. 

I'd like to learn about these things and although I know little about it now I grasp things like this pretty quickly. I'm not going to do anything silly though. I've had enough shocks to know I don't much like them. I found a retired audio engineer who liked to tinker a few years ago who looked at an amp for me, I might see if he's still tinkering. 

Ideally, and this may seem mad or just plain unfeasible, I like to take out the solid state pre and put my Peavey valve pre in, remove all the unnecessary inputs just leaving one and then build a shiney housing to show off the valves, like the Ashdown Little Bastard with the top removed. 

 

I'd say re-working the Peavey wouldn't be the most sensible route - it's a hybrid preamp which will have its own power supply requirements and is likely to be built around one large PCB, making it difficult to rehouse. 

With my own Dynacord, I started by making sure the amp was fully checked over and working in stock form, before building a new valve preamp from scratch to a relatively simple design. 

[Maude]

Yes, this is all just thinking out loud at the moment, I'll get the amp checked over before I do anything and see what it's like with one of the celestions in a cabinet.

Are you 'Mart the Hat' BTW? 

[Beer of the Bass]

I think I used that name in one or two places, yeah! I used to wear hats a lot...

[Happy Jack]

I had several vintage Dynacord valve amps some years ago, all very Germanic ... bullet proof and built like tanks, but also alles ist richtig = we don't do distortion.

These were some of the cleanest valve amps I've ever played a bass through, but in truth they didn't sound as 'rock' as my old Selmer and WEM amps.

 

[Maude]

22 hours ago, Beer of the Bass said:

I think I used that name in one or two places, yeah! I used to wear hats a lot...

I'm not a stalker, just googling for info and found a thread on a Telecaster forum which matched your posts above 👍

[Maude]

22 hours ago, Happy Jack said:

I had several vintage Dynacord valve amps some years ago, all very Germanic ... bullet proof and built like tanks, but also alles ist richtig = we don't do distortion.

These were some of the cleanest valve amps I've ever played a bass through, but in truth they didn't sound as 'rock' as my old Selmer and WEM amps.

 

Bullet proof is good, super clean is not what I want to hear about a valve amp. Having no input gain to drive it harder doesn't help I suppose, but a valve pre amp built in that could be driven may help. I've got my PJB for super clean, I want some old valve warmth from this. 

I'm going to try it at the weekend with a cab and put a pre amp pedal in front of it just to see whether it's worth persuing. Else I'll end up spending money and time on a really cool looking amp that sounds meh. 

[Happy Jack]

Try swopping out the Telefunken valves for some higher-gain models. A German engineer in a white lab-coat looking over your shoulder might not approve, but it's easy enough to get the sound you're after with a bit of experimentation.

[Beer of the Bass]

35 minutes ago, Happy Jack said:

Try swopping out the Telefunken valves for some higher-gain models. A German engineer in a white lab-coat looking over your shoulder might not approve, but it's easy enough to get the sound you're after with a bit of experimentation.

Only one half of the ECC81 is acting as a gain stage in these (the other half is a cathodyne phase inverter which has no gain whichever valve is used), and the power amp uses a lot  of negative feedback to keep it clean and linear.  So I'd say there's not a lot of potential to get dirt out of these with valve swaps alone. 

My own Eminent II that I built a new preamp into will get just a little grit, but it's all from the preamp.  Though it's a pretty fun sound and it's only really the mid control and DI outs that cause me to favour my Ampeg PF50T over the modded Dynacord.

[Maude]

I've given the amp a good clean up inside and had a look around to see if anything obvious was amiss. Now as I said I'm no amp tech but I couldn't see any obvious issues, burnt terminals or boards, swollen components or anything like that, and I know you can't tell much like that but it worked when it went into storage years ago and has been dry and warm indoors, the trunk it was in is beside the fireplace with a woodburner in, so I've dug out my old cabs with the celestion speakers in and given it a low volume test at home. The speakers are old Rola Celestion G15-150 8ohm, this is a guitar speaker but I used to use a pair of them for the bottom end of my bi-amped rig, basically they were used as subwoofers and that rig sounded amazing and was seriously loud, size and weight stopped me using it. I know they weren't handling full range as I'm asking of them now but surely the bottom end is the end that would've killed them if bass was going to? 

Anyway I'm going to take it all to rehearsal this week and try it at volume. The 15's are both in separate cabs and I can't remember if I wired the sockets to join them in parallel or series so the easiest way I'm guessing is to plug them both into the amp separately, each into one of the 8ohm outs on the back, I assume I can plug two cabs in at once. I might only need one but I'll take them both in case. (EDIT) I was having a dumb moment, they must be in parallel to give 4ohm, there's no reason I'd have wanted 16ohm, for a moment of stupidness I though 8 or 4 but obviously it would be 16 or 4.

At home I tryed it with a P bass with flats and one of the Celestions and it really sounded quiet nice, a valve pre would obviously improve it but it was warm and vintage with plenty of thump, I was a bit surprised actually as I though it might be a bit quiet and middy but no. I banged through 'Get Ready' by The Temptations and it sounded bang on, until Mrs. Maude reprimanded me 😁

If it behaves at volume and sounds nice then I'll get it checked over properly and replace anything it needs. 

 

Edited October 13, 2019 by Maude
My own stupidity.

[Maude]

One more question. Is there any real world gains to plugging both 15s (piggy backed in parallel) into the 4ohm out, over plugging them individually into the pair of 8ohm outs? 

Will using them in the 4ohm out pull more power out of the amp? 

[Beer of the Bass]

3 hours ago, Maude said:

One more question. Is there any real world gains to plugging both 15s (piggy backed in parallel) into the 4ohm out, over plugging them individually into the pair of 8ohm outs? 

Will using them in the 4ohm out pull more power out of the amp? 

 

Ah, glad it's working and sounding good! I wonder if the preamp differences between this and the Eminent make it a bit nicer sounding for electric bass (the Eminent being more geared towards being a PA mixer amp. 

I'd use the 4 ohm output when using both drivers, as the two 8 ohm outputs will be connected to the 8 ohm tap, so a 4 ohm load will be a mismatch.  That probably won't kill anything, but does run your output valves a little harder than they need to and may lose some power too.

[Maude]

Thanks for that, I thought using the 4ohm would be best and possibly give more power if using both cabs. 

The plan, sort of, is to build a flip top combo with the amp and one driver, but if I've got another driver kicking about then I may as well make a second, matching extension cabinet. 

All this is relatively pointless as they won't get used in either band I'm in at the moment. One band I use EB and go direct through the PA with a floor monitor and the second band I solely use DB through my PJB rig and can't see valve driven 15s being much good for that. It's purely for fun and I need to do something with this gear that has very little resale value, so I may as well make something cool. 

If it behaves at rehearsal and sounds good then it's game on. 🙂

[Maude]

After a bit of investigating I think these speakers are from the late sixties from the Rola Celestion labels, in 1970 the company was merged with another company and renamed Celestion Industries, then later in the seventies to Celestion International. 

I've found a page of serial numbers with dates so when I take the speakers out hopefully the stamp will still be on the gasket. 

It doesn't matter but there's something cool about have speakers a similar vintage to the amp rather than modern ones. 

 

 

[VTypeV4]

Nice amp - love stuff like this..

As for your Celestions, they're at least mid seventies if not early eighties - that frame gives it away. Look up the 'T' number - it'll be on the frame or cone somewhere - and msg Celestion, they're usually pretty helpful..