Moderators: pompeiisneaks, Colossal
It does seem I'm seeing more frequent reports of problems with Heyboer's lately. Mostly mechanical buzzing.M Fowler wrote:I will tell you this that I'm staying away from Heyboer TW iron my track record with their buzzing PT has to be due to ramping up production because they sure didn't have that problem before.
I like Allyn's Pacific set, Edcor, rj's Pacific iron and old audio equipment iron.
Mark
Well, I just need to know whether this thing will be usable. The radio sported some pretty funky 5 pin tubes, I think. I just hope it has the proper heater windings and a suitable B+.M Fowler wrote:The last Motorola amp I used the whole amp just added a 1/4 input jack and 1/4 speaker jack. It was basically a PTP Deluxe PP-6V6's.
No reason not to use old iron.
I got coupe of them like that which need to be re-potted. Hum bands were loose on them as well though tighten them didn't do much.It does seem I'm seeing more frequent reports of problems with Heyboer's lately. Mostly mechanical buzzing.
What causes this, loose windings?
Actually, Ken worked out that problem quite well and it really only applied to the Rocket, being the only tube rectified model. Leaving a cap on the hot side of the standby keeps the rectifier from having to charge the reservoir cap every time it's switched, so it isn't stressed every time. With this configuration 'hot switching' is not an issue. To alleviate the problem of a full charge on the reservoir when switched off, bleeder resistors were installed and offer noiseless switching as well as discharging the caps. As for the Express and Liverpool, the 25 watt resistor halted the inrush current from, as Merlin says, causing flashover in the valves, but what Merlin says about the choke is left up to debate, as Ken did what Merlin advises against. I don't think it's a problem.Mark wrote:Hi Lefty
Mechanical buzzing, that is buzzing with the standby switch set to off is the laminations of the transformer vibrating. You can try tightening the bolts holding the transformer together. The recommended action is to return it to Heyboer for repair/replacement. This sort of thing can happen after many years of use, not when the transformer is new.
Also completely off topic, while we are talking about tube experts. I noticed Merlin Blewcowe's site had this article, as usual Merlin's stuff is great. I'm wondering why Dumble and Fischer didn't work this out?
http://www.valvewizard.co.uk/standby.html
Actually, there isn't much to disagree about.Mark wrote:Thanks for the reply Blackburn, with respect I disagree. I think Ken knew he was using the 5AR4 beyond it's capabilities and to use only Mullard diodes is also a poor design choice as the component is operating on the edge of it's limits or beyond them depending on the individual component. As far as the standby switch goes I think knew this was a bad choice and it should only be used to turn the amp on, to turn the amp off the mains switch should be used.
https://tubeamparchive.com/files/taylor ... 08_758.pdf
Blencowe states:
The worst place for a standby switch is immediately in series with a smoothing choke: When the switch is thrown one end of the choke is left completely unconnected to anything. Not only is this likely to lead to pop sounds, but the choke will develop a massive fly-back voltage which can cause serious arcing in the choke and switch, and may even break through the choke insulation. This could be allayed by adding a snubbing diode in parallel with the choke (as shown), but this is still a pretty poor design choice.
Whether this has been a problem for Rocket owners I don't know, but it is a poor design choice as Blencowe states. Rocket owners should be encouraged to at least use a free wheeling diode to control the fly back voltage off the choke.
I'm not out to pour derision upon Ken, but to recognise the limits in his circuits which can be improved upon. We don't see to have a problem with putting VVR in these amps, but improving simple errors seems to be off limits. I think Blencowe's idea of using a 100K resistor in series with standby switch is a good idea.
There is also the matter of limiting resistors when using a valve rectifier which Ken doesn't use, but Dumble did use in his Manzamp.
http://www.valvewizard.co.uk/fullwave.html
Blencowe states:
A valve rectifiers must have a resistance in series with each anode. Many 'classic' amps do not include these when they ought to, and rectifier failure is common in these amps. The data sheet will provide a Minimum Limiting Resistance (Rlim(min)) for different supply voltages, although the limiting resistance can be decreased if the reservoir capacitor is also decreased proportionately. Part of the limitng resistance will be made up of unavoidable transformer resistance and reflected impedance, and this should be calculated first in order to find out whether any additonal resistance must be added.
For example, when supplied by a transformer rated at 300-0-300Vrms, the EZ80 specifies Rlim(min) = 215 ohms per anode. The total impedance presented to the rectifier by the transformer is given by:
Rt= Rs + (n^2)* Rp
Where:
Rs = DC resistance of one half of the transformer secondary winding.)
Rp = DC resistance of the transformer primary winding.
n = Secondary to primary turns ratio (equal to the secondary voltage divided by the primary supply voltage).
If we were using a mains transformer with a 240V; 80R primary and a 310-0-310V; 50R per half secondary:
Rt= 50 + (1.29^2)* 80 = 183R
The EZ80 requires at least 215 ohms, so an additonal 215 - 183 = 32 ohm resistor must be placed in series with each anode (so we would probably use 33 or 47 ohms).
Because the limiting resistors will have to carry the ripple current of the reservoir capacitor it is best to use high wattage resistors. Even 7W resistors will usually get quite warm. Remember that the voltage drop across the limiting resistors will cause the HT fall proportionately.
Alternatively, a single limiting resistor could be placed between the transformer centre tap and ground, although its power dissipation will be doubled.
Clearly your choice of rectifier has a huge effect on the HT you ultimately achieve. It is the voltage drop across the rectifier and series limiting resistance that causes 'sag' in Class-AB amps. When a loud sound is played and the amp suddenly draws more current the voltage dropped across the rectifier increases, lowering the HT and creating a compressing effect known as 'sag'. Class-A amps do not exhibit this effect since their current draw remains constant on average. Silicon diodes have a voltage drop (about 0.7V) that is constant with current so they do not produce sag, but it can be simulated simply be placing a resistor (roughly 100R to 330R) in series with the rectifier. But be sure to calculate the necessary power rating! A resistor in this position will usually need to be the biggest one in the amplifier, and may need to be rated at 10W or more.
Given that the Rocket uses such a large filter cap, the use of limiting resistors is probably something that should be considered by Rocket builders.
Just a few thoughts on Trainwreck choice of components as well as modifications.
I happen to agree with you mostly, however I forgot to mention in my post about the Rocket also being the only TW with a choke. We may never know what Ken might have said about using the standby to his very few Rocket customers, but I completely agree that using 80uf, being the maximum design center for a 5AR4, is too risky, you know, with drift and what not. I personally use 47uf for the reservoir with most of my amps with a tube rectifier. As far as tying the choke to the standby, Ken did this on the Rocket and I had one of Dr. Zs Mazerati GTs that also exhibited this and he doesn't leave a cap on the hot side of the standby, so there were plenty of pops and all that, but, I've talked to a friend that's been doing electronic work since the 50s, mentioning 'flashover' and 'flyback' and the conundrum of using the choke that way and he doesn't consider it an issue. With so many designs this way I don't worry too much either. I know what Merlin says and he does know his shit, but many things are simply and quite commonly disagreed upon, even by some of the best of them. I don't build amps with standby switches if they don't need them. My Rocket doesn't have one and when I had my Mazerati Gt, I didn't use it either. Very few tube rectifiers require one. Even with SS rectification, I'd still prefer a brimistor anyway. 
Well I think your Rocket is real, no? If so, there's really only one thing to say... Enjoy it you lucky son of a bitch! Just kiddin man. You should post a pic!2tone wrote:I know Ken was fully aware of the design limits etc, but he never stressed a caution with the standby switch, but did say it's better to leave it on when turning the amp off. I've played my Rocket for 22 years, using the standby switch between sets etc, and have had one rectifier go bad. I did change them after about 5 years tho for safety. So for me this whole thing has not been an issue.....I do use Mullard rectifiers..
We want pics and clips!2tone wrote:It's real(1991) and it's been converted to high voltage since about 1995! Runs around 350 v on plates(increased cathode resistor). Still no problems, and I've played it a lot....
Really interesting about the higher plates. I'm assuming Ken did that. Was it your idea or his? I actually just had this little fiasco with my AC30 build because of the PT being too high. Dissipating like 18 watts a piece! I'll be getting a proper one in a few days. I agree with Lefty... WE WANT TO SEE YOUR ROCKET!!!2tone wrote:It's real(1991) and it's been converted to high voltage since about 1995! Runs around 350 v on plates(increased cathode resistor). Still no problems, and I've played it a lot....
